Antidepressant medications

Antidepressant medications, referred to in psychiatry as thymoleptics, belong to group N06A according to the ATC classification and constitute one of the foundations of pharmacotherapy for affective disorders. Their history dates back to the 1950s, when the antidepressant properties of iproniazid (a MAOI) and imipramine (a TCA) were discovered by chance—findings that initiated a revolution in the treatment of depression and provided the first empirical basis for the monoamine hypothesis of depression. Since then, the pharmacology of antidepressants has evolved from non-selective compounds associated with numerous side effects, through selective reuptake inhibitors, to modern therapies targeting glutamatergic, melatonergic, and neuroactive steroid pathways.

This article provides a comprehensive, evidence-based overview of all classes of antidepressants, their mechanisms of action, clinical effectiveness, safety profiles, and indications. It is intended both for patients seeking reliable information and for clinicians in need of an up-to-date review of the subject. The article complements information on depression treatment, types of depression, and psychotherapy available on this platform.

Antidepressants – market data

Antidepressants are among the most commonly prescribed medications worldwide. The global antidepressant market was valued at approximately USD 17.8–18.7 billion in 2024, with projections indicating growth to USD 30–37 billion by 2033–2034, at a compound annual growth rate (CAGR) of around 7.5% [M1, M2]. The largest market—North America—accounts for approximately 42% of global revenue, with the U.S. market alone valued at around USD 6.8 billion in 2024 [M2]. SSRIs dominate, representing over 50–55% of all prescribed antidepressants [M1, M2]. A rapidly expanding segment includes fast-acting glutamatergic antidepressants—such as esketamine and oral pipeline candidates—with a projected CAGR of approximately 6.9% through 2030 [M3].

The epidemiological data driving this market growth are clear: depression affects approximately 280–300 million people globally, and the COVID-19 pandemic increased the global prevalence of depression and anxiety disorders by about 25% in its first year (WHO, 2021). In the United States, the proportion of adults using antidepressants rose from 13.6% (2015–2018) to 16.5% in 2020, while the number of monthly prescriptions increased by over 66% between 2016 and 2022 [M2]. In Poland, detailed epidemiological data on antidepressant prescriptions are not publicly available at a comparable level of granularity; however, an increase in reimbursement and consumption of psychotropic medications over the past decade has been documented in reports from the National Health Fund (NFZ).

Market growth is driven by several factors: increasing awareness of mental health and the destigmatization of psychiatric treatment, population aging (with depression being one of the most common disorders among older adults), the expansion of telemedicine (with over 60% of psychiatric visits in the U.S. conducted by phone or online), the availability of generic medications significantly reducing treatment costs, and the emergence of new therapies for treatment-resistant depression, which previously remained difficult to manage effectively. At the same time, the market faces challenges, including the expiration of patents on key compounds, pricing pressure from generic manufacturers, and growing concerns regarding the long-term tolerability of antidepressant medications.

Neurobiological basis of antidepressant action

For decades, the dominant model of depression pathogenesis was the monoamine hypothesis, which assumes that low mood results from a deficiency of serotonin, norepinephrine, and/or dopamine in the synaptic cleft. This assumption underlies the mechanism of action of most classical antidepressants—SSRIs, SNRIs, TCAs, and MAOIs—whose common denominator is increasing the availability of monoamines in the synaptic space. While this hypothesis explains why these medications are effective, it does not fully account for the delayed onset of their clinical effects (typically 2–4 weeks), given that neurotransmitter levels increase within hours of the first dose [1].

Contemporary understanding of antidepressant mechanisms is significantly more complex. Key elements include: (1) receptor-level adaptations occurring over weeks at both pre- and postsynaptic sites—such as desensitization of 5-HT1A and α2 autoreceptors, leading to increased serotonergic tone; (2) neuroplasticity—particularly the influence on brain-derived neurotrophic factor (BDNF) and hippocampal neurogenesis, well documented for SSRIs, SNRIs, and mirtazapine; (3) modulation of the hypothalamic–pituitary–adrenal (HPA) axis and normalization of cortisol hyperactivity; and (4) anti-inflammatory effects—specifically the reduction of pro-inflammatory cytokines (e.g., IL-6, TNF-α) observed across multiple classes of antidepressants [2]. The discovery that esketamine (an NMDA receptor antagonist acting on the glutamatergic system) produces antidepressant effects within hours has expanded the model to include rapid synaptic changes dependent on mTOR and AMPA pathways—independent of the monoaminergic system [3].

From a clinical perspective, the multiplicity of mechanisms implies that lack of efficacy in one class of antidepressants does not predict failure of another. A patient who does not respond to an SSRI may still benefit from an SNRI, mirtazapine, agomelatine, or augmentation strategies such as lithium—often because a different neurobiological substrate predominates in their form of depression. This principle is central to rational treatment sequencing in cases of treatment-resistant depression.

Effectiveness of antidepressants – what do the meta-analyses say?

The largest and most widely cited study on the effectiveness of antidepressants is the network meta-analysis by Cipriani et al., published in The Lancet in 2018, which included 522 randomized clinical trials with 116,477 participants and compared 21 antidepressant medications [4]. The results clearly confirmed that all 21 evaluated antidepressants were more effective than placebo in the treatment of acute major depressive episodes. The odds ratio for treatment response ranged from 1.37 (reboxetine) to 2.13 (amitriptyline), indicating that patients treated with antidepressants were approximately 1.5 to 2 times more likely to respond than those receiving placebo [5]. In terms of both efficacy and acceptability, escitalopram, sertraline, venlafaxine, mirtazapine, and agomelatine stood out, while reboxetine showed the lowest efficacy profile.

An important perspective for interpreting these results lies in the fact that the overall standardized mean difference (SMD) for antidepressants versus placebo in reducing depression severity was 0.30, which falls within the range of a small effect according to Cohen’s scale. However, when the same dataset is transformed into response and remission rates, the results appear substantially more robust: most antidepressants were associated with more than a 50% higher response rate compared to placebo, and over half were associated with more than a 50% higher remission rate [5]. The difference between these interpretations stems from the mathematical properties of the measures—SMD is more sensitive to outcome heterogeneity, whereas odds ratios better reflect the clinical probability of success for an individual patient.

Highly relevant for clinical practice are findings from a meta-analysis published in Molecular Psychiatry (2022), focusing on the continuation phase of treatment. This analysis included 34 studies (n=9,384) and 20 antidepressants, demonstrating that continuing antidepressant treatment after achieving remission significantly reduces the risk of relapse compared to switching to placebo. For most medications, the risk of relapse in the placebo group was two to three times higher than in the continuation group [6]. This provides a key argument for both clinicians and patients who may consider discontinuing medication after initial improvement.

An updated review of treatments across varying depression severity levels (published in eClinicalMedicine in 2024, including 676 RCTs and 105,477 participants) yielded an important clinical conclusion: in mild depression, antidepressants did not demonstrate a significant advantage over placebo, whereas psychotherapy (particularly group-based CBT) and selected approaches such as yoga or guided self-help were effective. In more severe depression, antidepressants—either as monotherapy or in combination with psychotherapy—remain evidence-based and effective treatment options [10]. These findings have direct implications for clinical guidelines: in mild to moderate depression, psychotherapy may be considered a first-line treatment, while pharmacotherapy should be viewed as a complementary or alternative option.

SSRIs – selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are the first-line treatment in the pharmacotherapy of depression and remain the most commonly prescribed class of antidepressants worldwide, accounting for over 50% of the global antidepressant market. Their mechanism of action involves the selective inhibition of the serotonin transporter (SERT) in the presynaptic neuron, which increases serotonin levels in the synaptic cleft and gradually modulates the activity of the serotonergic system. This selectivity for serotonin (in contrast to tricyclic antidepressants) translates into a significantly improved tolerability profile, including the absence of anticholinergic effects, lower cardiovascular risk, and a reduced potential for fatal overdose [7].

The SSRI group includes fluoxetine (Prozac; the longest half-life—approximately 1–4 days; lowest risk of discontinuation syndrome), sertraline (one of the most widely used antidepressants in many countries; favorable drug interaction profile), escitalopram (considered the most selective SSRI with an excellent tolerability profile; in Cipriani’s meta-analysis, it showed one of the best balances between efficacy and acceptability), citalopram (safe in coronary artery disease; requires caution in patients with prolonged QTc), paroxetine (strong anticholinergic effects; higher risk of discontinuation syndrome; often used in anxiety disorders and PTSD), and fluvoxamine (preferred in OCD; associated with multiple CYP450 interactions). All SSRIs have demonstrated efficacy not only in depression but also in anxiety disorders, OCD, PTSD, social anxiety disorder, and—in the case of paroxetine—premature ejaculation [4, 7].

The most common side effects of SSRIs include nausea and gastrointestinal discomfort (particularly at the beginning of treatment, usually resolving within 1–2 weeks), sexual dysfunction (anorgasmia, reduced libido, delayed ejaculation), affecting approximately 30–40% of patients and often representing a major reason for early discontinuation, excessive sweating, insomnia or hypersomnia, and tremor. Less frequently, hyponatremia may occur, especially in older adults. The risk of serotonin syndrome increases when SSRIs are combined with other serotonergic agents (such as tramadol, triptans, or MAOIs—the latter being absolutely contraindicated). All SSRIs carry an FDA “black box” warning regarding an increased risk of suicidal thoughts in children, adolescents, and young adults up to 25 years of age, particularly during the initial weeks of treatment, which necessitates close clinical monitoring in this population [4].

SNRI – serotonin and noradrenaline reuptake inhibitors

Serotonin–norepinephrine reuptake inhibitors (SNRIs) inhibit the reuptake of both serotonin and norepinephrine, which may explain their advantage over SSRIs in certain clinical contexts. Their dual action on serotonergic and noradrenergic systems is associated with improved outcomes in patients presenting with predominant apathy, fatigue, and psychomotor slowing (reflecting the noradrenergic component), documented efficacy in the treatment of neuropathic pain and fibromyalgia (particularly for duloxetine and venlafaxine), and potentially greater effectiveness in severe depressive episodes. In the Cipriani meta-analysis, venlafaxine demonstrated higher efficacy than several SSRIs, although the differences were moderate [4].

Venlafaxine (Effexor, Velafax) is available in immediate-release (IR) and extended-release (XR) formulations; at lower doses (around 75 mg), it primarily exerts serotonergic effects, while noradrenergic activity becomes more pronounced at higher doses (150–225 mg). It is used in depression, generalized anxiety disorder, social anxiety disorder, and PTSD. Caution is required in patients with hypertension, as venlafaxine may increase blood pressure, especially at higher doses. It is also associated with a higher risk of discontinuation syndrome compared to SSRIs. Duloxetine (Cymbalta) provides a more balanced serotonergic and noradrenergic effect across therapeutic doses and is approved for the treatment of depression, neuropathic pain, fibromyalgia, and stress urinary incontinence. Milnacipran and its isomer levomilnacipran exhibit a stronger noradrenergic than serotonergic effect and are used in fibromyalgia and depression. Desvenlafaxine (the active metabolite of venlafaxine) is characterized by lower pharmacokinetic variability and a reduced potential for drug interactions [7, 8].

Adverse effects of SNRIs include those typical for this class: nausea (more frequent than with SSRIs), elevated blood pressure (requiring monitoring, particularly with venlafaxine at doses above 150 mg), sexual dysfunction (similar to SSRIs), excessive sweating, and urinary retention. Absolute contraindications include concurrent use with MAO inhibitors due to the risk of hypertensive crisis and serotonin syndrome. SNRIs should be discontinued gradually, with dose tapering, to minimize the risk of discontinuation symptoms.

TCAs – tricyclic antidepressants

Tricyclic antidepressants (TCAs) were the standard of pharmacotherapy for depression for decades following their discovery in the late 1950s. Their mechanism of action is multimodal: inhibition of serotonin and norepinephrine reuptake (similar to SNRIs), combined with antagonism at muscarinic (M1), histaminergic (H1), adrenergic (α1), and sodium channels (Na+ blockade). This broad pharmacological profile explains both the high clinical efficacy of TCAs and their burdensome side effect profile [7, 8].

Key active substances include amitriptyline—the most effective antidepressant in the Cipriani meta-analysis (OR 2.13), but also one of the least well tolerated due to adverse effects; it is also used in migraine prophylaxis, neuropathic pain, and insomnia. Imipramine represents the historical “gold standard” in depression research. Clomipramine is considered a first-line treatment in obsessive-compulsive disorder (OCD). Desipramine is more selective for norepinephrine and better tolerated than amitriptyline. Doxepin has strong sedative and antihistaminergic effects and is approved at low doses for insomnia. Nortriptyline, an active metabolite of amitriptyline, is somewhat better tolerated. Opipramol, an atypical TCA, acts mainly via sigma and histamine receptors and is used in somatization disorders and anxiety. Tetracyclic antidepressants, such as maprotiline, exhibit a similar profile to TCAs, with a predominance of noradrenergic and sedative effects.

The adverse effects of TCAs limit their use as first-line treatments. Anticholinergic effects include dry mouth, constipation, urinary retention, visual disturbances, and cognitive impairment. Orthostatic hypotension increases the risk of falls, particularly in older adults. Sedation (via H1 antagonism) may be beneficial in patients with insomnia but can impair daytime functioning. Cardiotoxicity is a major concern—due to sodium channel blockade, TCAs can prolong QRS and QTc intervals and increase the risk of ventricular arrhythmias; they are contraindicated in patients with recent myocardial infarction or significant cardiac arrhythmias. TCAs are particularly dangerous in overdose, as the therapeutic and lethal doses are relatively close, making them high-risk medications in patients with suicidal tendencies. Current clinical guidelines reserve TCAs for treatment-resistant depression, melancholic or psychotic depression (in combination therapy), neuropathic pain, OCD (clomipramine), and selected neurological indications.

NARI – selective noradrenaline reuptake inhibitors

Norepinephrine reuptake inhibitors (NARIs) selectively inhibit the reuptake of norepinephrine via the norepinephrine transporter (NET), without significantly affecting the serotonin transporter (SERT). The only clinically available NARI is reboxetine. In theory, its selective noradrenergic action should be particularly beneficial for symptoms such as psychomotor slowing, apathy, impaired concentration, and reduced drive. However, in clinical practice, reboxetine demonstrated the lowest efficacy profile among all antidepressants evaluated in the Cipriani meta-analysis, being the only medication that performed significantly worse than all others [4].

Reboxetine is approved in Poland for the treatment of major depressive disorder, but its use is generally limited to cases where other classes of antidepressants have proven ineffective or poorly tolerated, or when selective enhancement of motivation and concentration is specifically desired. Its side effect profile includes dry mouth, urinary retention, constipation, insomnia, and sweating. It does not exhibit significant cardiotoxic effects. In clinical practice, it is rarely used as a first-line treatment and is increasingly uncommon even as a second-line option in the era of more robustly supported alternatives.

NDRI – noradrenaline and dopamine reuptake inhibitors (bupropion)

Bupropion—the only clinically available norepinephrine–dopamine reuptake inhibitor (NDRI)—is pharmacologically distinct from other antidepressants. It inhibits the reuptake of norepinephrine and dopamine without significantly affecting serotonin. This results in a unique clinical profile: it has a relatively low impact on sexual function (rarely causing sexual dysfunction, which distinguishes it from SSRIs and SNRIs), does not promote weight gain (and may even support weight reduction), and has activating properties (making it preferable in patients with predominant apathy and fatigue). It is approved for the treatment of major depressive disorder, seasonal affective disorder (SAD), and—uniquely—nicotine dependence [9].

Bupropion is available in Poland, although it is not typically used as a first-line monotherapy for depression. Its specific therapeutic role includes patients with depression and SSRI/SNRI-induced sexual dysfunction (either as a switch or augmentation), patients with SAD, and those with coexisting nicotine dependence and depression. The most common side effects include insomnia, agitation, dry mouth, and headaches. The most important limitation is its effect on lowering the seizure threshold—bupropion is contraindicated in patients with epilepsy, anorexia nervosa, or bulimia (conditions associated with increased seizure risk), as well as during withdrawal from alcohol or benzodiazepines. The maximum safe daily dose should not exceed 450 mg (extended-release form), due to a dose-dependent increase in seizure risk [9].

MAOIs – Monoamine Oxidase Inhibitors: Effectiveness and Limitations

Monoamine oxidase inhibitors (MAOIs) are the oldest class of antidepressants, acting by inhibiting the enzyme monoamine oxidase (MAO), which is responsible for the breakdown of serotonin, norepinephrine, and dopamine. Clinically, they are divided into non-selective, irreversible MAOIs (phenelzine, tranylcypromine, isocarboxazid) and selective, reversible MAO-A inhibitors (such as moclobemide, which is available in Poland). Non-selective MAOIs are highly effective, particularly in atypical depression (characterized by mood reactivity, hypersomnia, increased appetite, and rejection sensitivity), where meta-analyses suggest superiority over TCAs. They are also used in treatment-resistant depression and social anxiety disorder [7].

However, their use is limited by the significant risk of hypertensive crises related to tyramine intake. Non-selective inhibition of MAO-A in the gastrointestinal tract prevents the metabolism of dietary tyramine, which can lead to a sudden and potentially life-threatening increase in blood pressure. The requirement for a strict dietary regimen (avoiding aged cheeses, fermented products, red wine, pickled foods, yeast products, and smoked fish and meats) represents a major barrier to their use. Moclobemide, as a selective and reversible MAO-A inhibitor, largely avoids this issue—tyramine can still be metabolized via MAO-B, and the reversible nature of inhibition reduces risk. It has demonstrated efficacy in depression, particularly atypical forms and those with prominent anxiety symptoms.

Absolute contraindications for all MAOIs include concurrent use with SSRIs, SNRIs, tramadol, triptans (due to the risk of potentially fatal serotonin syndrome), sympathomimetics, and pethidine. Appropriate washout periods are essential when switching treatments—for example, at least 14 days should elapse after discontinuing a non-selective MAOI before initiating another antidepressant.

Mirtazapine and drugs with a mixed receptor profile

Mirtazapine is an antagonist of presynaptic α2-adrenergic receptors (which increases the release of norepinephrine and serotonin by removing autoreceptor inhibition) as well as postsynaptic 5-HT2 and 5-HT3 receptors. Its action on the 5-HT3 receptor results in a lower risk of nausea and gastrointestinal side effects compared to SSRIs and SNRIs. Strong H1 receptor blockade explains its pronounced sedative effects and appetite stimulation—clinically beneficial in patients with insomnia, anxiety, and weight loss (particularly in older adults and in depression with cachexia), but potentially problematic in patients with a tendency toward overweight. In the Cipriani meta-analysis, mirtazapine ranked among the top antidepressants in terms of efficacy [4].

Mirtazapine is used as monotherapy or as an augmentation strategy with SSRIs or SNRIs—particularly in combination with venlafaxine (often referred to as “California Rocket Fuel”), which has demonstrated higher efficacy than monotherapy in clinical studies, albeit with increased treatment complexity. Adverse effects include sedation (via H1 blockade—beneficial for insomnia but potentially impairing during the day), weight gain (due to H1 and 5-HT2C antagonism), elevated cholesterol levels, and rarely agranulocytosis (requiring blood count monitoring if infection is suspected). It does not typically cause sexual dysfunction.

Trazodone (a SARI—serotonin antagonist and reuptake inhibitor) has strong sedative properties and is widely used at low doses (50–100 mg) to treat insomnia associated with depression; at higher doses, it acts as an antidepressant. A rare but serious adverse effect is priapism.

Agomelatine – melatoninergic drugs and their special place in therapy

Agomelatine (Valdoxan) represents a fundamentally different pharmacological strategy. It acts as an agonist of melatonin receptors MT1 and MT2 (affecting circadian rhythms and sleep architecture) and as an antagonist of serotonin 5-HT2C receptors (which increases dopamine and norepinephrine release in the prefrontal cortex without directly affecting serotonin levels). It does not inhibit the reuptake of any neurotransmitter, resulting in a distinct side effect profile compared to SSRIs and SNRIs: no sexual dysfunction, no weight gain, and no discontinuation syndrome upon cessation. Improvements in sleep architecture (shortened sleep latency and increased slow-wave sleep) can occur within the first days of treatment, potentially enhancing subjective well-being earlier than mood improvement. In the Cipriani meta-analysis, agomelatine ranked highly in terms of acceptability and was among the top medications for balancing efficacy and tolerability [4].

A key clinical limitation of agomelatine is hepatotoxicity. Elevated liver enzyme levels are observed in approximately 1–3% of patients, and in rare cases may progress to clinically significant liver injury. Liver function tests are required before initiating treatment, and then at 3, 6, 12, and 24 weeks, followed by periodic monitoring thereafter. Agomelatine is contraindicated in patients with active liver disease or elevated baseline transaminases. It is available in Poland and reimbursed in selected indications. It may show synergistic effects when combined with non-pharmacological treatments, particularly light therapy and interventions focused on circadian rhythm regulation.

Esketamine and NMDA antagonists – a revolution in the treatment of drug-resistant depression

The year 2019 marked a breakthrough in the pharmacotherapy of depression: the FDA approved intranasal esketamine (Spravato, S-ketamine) as the first antidepressant in over 60 years with a fundamentally new mechanism of action—NMDA receptor antagonism within the glutamatergic system—for the treatment of treatment-resistant depression (TRD). In January 2025, the FDA expanded the indication of esketamine to include monotherapy in TRD, meaning that for the first time, treatment no longer required mandatory combination with an oral antidepressant. A randomized, double-blind, placebo-controlled trial (NCT04599855, n=378) demonstrated that esketamine at doses of 56 mg and 84 mg achieved the primary endpoint (MADRS score at 28 days) with differences versus placebo of −5.1 and −6.8 points, respectively (p<0.001), corresponding to effect sizes of 0.48 and 0.63 [11, 12, 13].

The key advantage of esketamine over conventional antidepressants is the speed of action: symptom improvement may occur within 24 hours of the first dose, making it particularly valuable in acute clinical situations, including patients with active suicidal ideation. Esketamine is one of the very few pharmacological agents—alongside lithium—with evidence supporting an anti-suicidal effect [14]. Its rapid mechanism involves the mTOR/AMPA signaling pathway: NMDA receptor antagonism initiates a cascade leading to rapid synthesis of synaptic proteins and restoration of synaptic plasticity within hours, which explains an antidepressant effect not achievable through monoaminergic modulation alone [3].

Practical limitations of esketamine include: (1) the requirement for administration in a certified medical facility under physician supervision for at least two hours post-dose (due to risks of sedation, dissociation, and respiratory depression); (2) adherence to the REMS (Risk Evaluation and Mitigation Strategy) protocol; (3) inability to drive or operate machinery for at least 24 hours after administration; and (4) high treatment costs. The standard protocol involves twice-weekly administration during the first four weeks (acute phase), followed by once weekly or once every two weeks during maintenance treatment [11, 12]. In Poland, esketamine is available to a limited extent, primarily in specialized psychiatric centers, and its accessibility remains significantly lower than in the United States and Western Europe.

Zuranolone – neuroactive steroids and a new approach to postpartum depression

Zuranolone (Zurzuvae) is the first oral neuroactive steroid approved by the FDA (August 2023) for the treatment of postpartum depression (PPD). Its mechanism of action differs from all previously described antidepressants: zuranolone acts as a positive allosteric modulator of GABA-A receptors, helping to normalize the disrupted inhibitory signaling of the GABAergic system associated with hormonal changes after childbirth. Key features include a short treatment course (14 days, once daily in the evening), rapid clinical effect (improvement observed as early as day 3), and high tolerability [15].

Zuranolone is particularly important as a therapeutic response to the unique biological challenge of PPD: the abrupt decline in neuroactive progesterone metabolites (such as allopregnanolone) after delivery, which destabilizes GABAergic transmission. Previously, the only treatment specifically approved for PPD was brexanolone (Zulresso)—an intravenous therapy requiring a 60-hour hospital stay. As an oral medication available through pharmacies, zuranolone significantly reduces barriers to access. It is not currently available in Poland (no EMA approval), and studies in European populations are ongoing. In a broader context, research into the role of neuroactive steroids in other forms of depression (such as MDD and SAD) is still underway.

Mood stabilizers and augmentation of pharmacotherapy for depression

In clinical practice—particularly in treatment-resistant depression (TRD) or bipolar disorder—antidepressant monotherapy is often insufficient. Lithium (lithium carbonate) is the first historically documented mood stabilizer, used both for mood stabilization in bipolar disorder and as an augmentation strategy in TRD. Importantly, it is one of the very few agents (alongside esketamine) with proven anti-suicidal effects—meta-analyses show a reduction in suicide risk of approximately 80% compared to no lithium treatment [16]. Its use requires regular serum level monitoring due to a narrow therapeutic window, as well as ongoing assessment of thyroid and renal function.

Augmentation of antidepressants with atypical antipsychotics (such as quetiapine, aripiprazole, olanzapine, and brexpiprazole) is a well-established strategy in TRD. Quetiapine, at augmentation doses (50–300 mg/day), is FDA-approved as an adjunctive treatment in major depressive disorder (MDD), as is aripiprazole. The mechanism of augmentation involves 5-HT2A receptor antagonism and partial D2 receptor agonism (in the case of aripiprazole), enhancing serotonergic and dopaminergic transmission in the prefrontal cortex. Other augmentation strategies include the addition of triiodothyronine (T3) in subclinical hypothyroidism, combining bupropion with SSRI/SNRI therapy, and using lamotrigine in bipolar depression. Polish clinical guidelines for depression pharmacotherapy (Samochowiec et al.) discuss these strategies within structured treatment sequencing for TRD [17].

Antipsychotic medications used in depression with psychotic features (such as sulpiride, levomepromazine, and flupentixol) represent a distinct clinical category. In such cases, the standard approach involves combining an antidepressant with an antipsychotic or using electroconvulsive therapy (ECT)—antidepressant monotherapy is not sufficient in psychotic depression. The need for combination therapy is often not well understood by patients and their families, making thorough psychoeducation essential.

Principles of antidepressant selection and time to therapeutic effect

The selection of an antidepressant should not be arbitrary or based solely on prescriber habit. Rational decision-making takes into account several key factors: the severity and symptom profile (e.g., predominant insomnia → mirtazapine or trazodone; apathy/psychomotor slowing → bupropion or an SNRI; neuropathic pain → duloxetine, venlafaxine, amitriptyline; atypical depression → MAOIs, escitalopram); previous treatment response (the strongest predictor); family history of response to specific medications; comorbid conditions (cardiovascular disease → avoid TCAs; epilepsy → avoid bupropion; liver disease → avoid agomelatine); potential drug interactions (paroxetine and fluoxetine are strong CYP2D6 inhibitors; fluvoxamine inhibits CYP1A2 and CYP3A4); side effect profile relevant to the patient (sexual dysfunction → bupropion, mirtazapine; weight gain → escitalopram, sertraline, and bupropion are generally safer than paroxetine or mirtazapine); as well as availability and cost [4, 17].

The delay in therapeutic response is one of the most challenging aspects of antidepressant treatment for both patients and clinicians. A full antidepressant effect typically requires 4–8 weeks of consistent use at an adequate dose. During the first days and weeks, side effects (especially nausea and agitation with SSRIs/SNRIs) may occur in the absence of meaningful clinical improvement—this is a common reason for premature discontinuation. Notable exceptions include esketamine (effect within 24 hours) and mirtazapine (sedative effect from the first dose, although antidepressant effects still take weeks). Early signs of response—such as improved sleep, reduced anxiety, and increased energy—often precede mood improvement by 1–2 weeks [4, 7].

A general clinical rule is that if there is no improvement after 4–6 weeks at an appropriate dose, a change or augmentation of treatment should be considered. If there is a partial response, it may be reasonable to continue treatment up to 8–12 weeks or introduce augmentation. After achieving remission, treatment should be continued for at least 6–12 months (in a first episode) or longer in recurrent depression. Maintenance-phase meta-analyses clearly show a significantly higher risk of relapse following premature discontinuation [6, 17].

Antidepressant Adverse Drug Effects – Summary and Management

Adverse effects of antidepressants are one of the main reasons for premature discontinuation and poor adherence to treatment. Understanding the side-effect profile of each class is essential both for clinicians when selecting a medication and for patients to know what to expect. The most important categories of adverse effects include:

Sexual dysfunction is among the most common and burdensome side effects of SSRIs and SNRIs, affecting approximately 30–40% of patients. It includes reduced libido, delayed orgasm/ejaculation, or anorgasmia. These symptoms are often underreported, as patients may feel uncomfortable discussing them and clinicians do not always ask proactively. Management options include dose reduction, switching to another medication (such as bupropion, mirtazapine, or agomelatine), adding bupropion as an augmentation strategy, or intermittent dosing (e.g., with fluoxetine). A particularly important phenomenon is post-SSRI sexual dysfunction (PSSD)—a rare but real condition in which sexual dysfunction persists after discontinuation of the medication, documented in the literature and requiring further research [4].

Weight gain is a significant long-term concern, particularly with paroxetine, mirtazapine, and amitriptyline (due to increased appetite and antihistaminergic effects). Bupropion and fluoxetine tend to have a neutral or slightly weight-reducing effect. Escitalopram and sertraline are relatively neutral in this regard. Sedation (seen with mirtazapine, TCAs, and trazodone) may be beneficial in patients with insomnia but can limit daytime functioning. Nausea and gastrointestinal discomfort associated with SSRIs/SNRIs are usually transient and resolve within 1–2 weeks; taking the medication with food and gradually titrating the dose can help minimize these effects. Less common but clinically significant adverse effects that require monitoring include hyponatremia (especially with SSRIs in older adults), increased bleeding risk (SSRIs inhibit platelet aggregation via serotonin depletion—caution is needed with NSAIDs, aspirin, and anticoagulants), and QTc prolongation (notably with citalopram >40 mg and escitalopram >20 mg—ECG monitoring recommended) [7].

Discontinuation of antidepressants – discontinuation syndrome

Antidepressant discontinuation syndrome is a clinically significant yet often misunderstood and underestimated phenomenon—both by some clinicians and patients. It refers to a characteristic set of symptoms that may occur after abrupt or overly rapid discontinuation of an antidepressant. These symptoms include anxiety, irritability, sleep disturbances, nausea, dizziness, “electric shock” sensations (dysesthesia, often described as “brain zaps”), flu-like malaise, and tearfulness. They may be mistaken for a relapse of depression, which can lead to unnecessary reinstatement of medication or unwarranted fear of “addiction” [7].

An important clarification is that discontinuation syndrome is not the same as addiction in the clinical sense—there is no craving, tolerance escalation, or compulsive drug-seeking behavior. Instead, it reflects physiological adaptation of the nervous system, which requires time to readjust after medication withdrawal. The risk and severity of symptoms depend on several factors: the drug’s half-life (highest risk with paroxetine and venlafaxine XR; lowest with fluoxetine), duration of treatment, dosage, and the speed of tapering. A safe discontinuation protocol involves gradual dose reduction—sometimes over weeks or even months in cases of long-term or high-dose treatment. In patients who struggle to discontinue paroxetine or venlafaxine, switching to fluoxetine (due to its long half-life) and then tapering may be an effective strategy [7, 17].

Special populations: pregnancy, breastfeeding, children, and older adults

Depression during pregnancy and breastfeeding

The decision to use pharmacotherapy for depression during pregnancy requires an individualized risk–benefit assessment, balancing the risks of untreated depression (for both mother and fetus) against the potential risks of medication. Sertraline and escitalopram have the most well-established safety profiles in pregnancy and are commonly used. SSRIs do not demonstrate significant teratogenic risk in the first trimester, although prolonged use in the third trimester may be associated with transient neonatal adaptation syndrome (irritability, sleep disturbances, feeding difficulties) and a small risk of persistent pulmonary hypertension of the newborn [8]. Tricyclic antidepressants are generally not recommended due to cardiotoxicity and anticholinergic effects. Decisions should be made collaboratively between a psychiatrist and an obstetrician, with thorough psychoeducation covering both treatment and non-treatment scenarios.

Antidepressants in children and adolescents

A network meta-analysis by Cipriani et al. (The Lancet, 2016) on depression in children and adolescents showed that antidepressant efficacy is lower in this population than in adults, with more pronounced differences between medications. Fluoxetine is the only SSRI fully approved for depression in children over the age of 8 and has the strongest evidence for efficacy. Combination therapy with fluoxetine and CBT yields better outcomes than monotherapy. Special caution is required due to the FDA “black box” warning regarding increased risk of suicidal thoughts in individuals under 25 years of age—this necessitates close clinical monitoring and family psychoeducation [8B].

Antidepressants in older adults

Pharmacotherapy of depression in older adults is complex due to polypharmacy (multiple drug interactions), altered pharmacokinetics (reduced hepatic metabolism, decreased renal clearance, increased CNS sensitivity), and a higher risk of specific adverse effects (hyponatremia with SSRIs, orthostatic hypotension with TCAs leading to fall risk, anticholinergic effects worsening cognitive impairment). Preferred options include escitalopram and sertraline (favorable interaction profile, minimal anticholinergic activity, no QT prolongation at therapeutic doses) and mirtazapine (especially when insomnia is present, provided fall risk is low). TCAs are generally discouraged in geriatric populations and are listed as potentially inappropriate medications (Beers criteria). Vascular depression in older adults, particularly associated with white matter lesions, requires a tailored approach and is often less responsive to standard antidepressants [7].

Pharmacogenetics of antidepressants – the era of personalization

One of the major challenges in antidepressant pharmacotherapy remains the unpredictability of response: the same drug and dose may lead to remission in one patient, be ineffective in another, and cause significant side effects in a third. Pharmacogenetics explores the genetic basis of these differences. The key genes involved include CYP2D6 (metabolism of most SSRIs, SNRIs, and TCAs) and CYP2C19 (metabolism of escitalopram, citalopram, and sertraline). Genetic polymorphisms classify patients as poor, intermediate, normal, or ultrarapid metabolizers, which can significantly alter drug concentrations at the same nominal dose [18].

In practice, this means that a CYP2D6 poor metabolizer may reach toxic plasma levels of paroxetine at standard doses, whereas an ultrarapid metabolizer may have subtherapeutic levels requiring higher doses. Pharmacogenetic testing (including CYP2D6 and CYP2C19 genotyping, and in more advanced panels also SLC6A4/5-HTTLPR) can support drug and dose selection. However, widespread implementation is still limited by cost, accessibility, and the lack of unequivocal prospective evidence demonstrating improved clinical outcomes.

Commercial tools such as GeneSight (USA) and other pharmacogenetic panels provide multi-gene analysis and guidance on likely patient response to specific antidepressants. The GUIDED trial (2019) showed higher response and remission rates when treatment was guided by pharmacogenetic testing compared to standard care. However, its methodology has been criticized, and independent replication is still needed [18]. Pharmacogenetics remains a promising but evolving field—already valuable in selected complex cases, but not yet ready for routine implementation as a standard of care.

PoSummary – antidepressant classes overview table

This article covers all major classes of antidepressants. More detailed information on specific groups can be found in extended guides on SSRI, SNRI, TCA, and NARI. See also related articles on long-term effects of antidepressants, depression treatment, and psychotherapy.

References and scientific sources

1. Stahl S.M. Stahl’s Essential Psychopharmacology. Cambridge University Press, 2021. cambridge.org
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11. SPRAVATO (esketamine) Prescribing Information. FDA, 2025. accessdata.fda.gov
12. Pharmacytimes.com: Esketamine Receives FDA Approval for Adults With Treatment-Resistant Depression (monotherapy, Jan 2025). pharmacytimes.com
13. Abbas M. et al. Esketamine for Treatment-Resistant Depression after failed ECT. PMC 2025. pmc.ncbi.nlm.nih.gov
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15. FDA News Release. FDA approves zuranolone (Zurzuvae) for postpartum depression. August 4, 2023. fda.gov
16. Cipriani A. et al. (meta-analysis lithium) – Nolen W.A. et al. Antisuicidal and mood-stabilising effects of lithium. J Affect Disord 2023. pubmed.ncbi.nlm.nih.gov
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Market data sources

21. [M1] Market.us. Antidepressants Drugs Market 2025. media.market.us
22. [M2] Market.us. Global Antidepressants Market (Nov 2025). media.market.us
23. [M3] Mordor Intelligence. Antidepressants Market Trends, 2025–2030. mordorintelligence.com