Antidepressants — Medication Guide, Uses & Safety — Uses, Dosage & Side Effects | MyMedicPlus

Antidepressants are a broad class of prescription medications used primarily to treat depression and a range of anxiety disorders. The most commonly prescribed types are selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs). Older classes include tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs), which are now used less frequently due to their more complex safety profiles. Newer atypical antidepressants include mirtazapine, bupropion, trazodone, and vortioxetine, which work through distinct or multiple mechanisms. Antidepressants act on neurotransmitter systems in the brain to improve mood, reduce anxiety, restore energy and motivation, and normalize sleep and appetite. A critically important point for patients is that antidepressants do not produce their full therapeutic benefit immediately — they typically require 4–6 weeks of consistent treatment before meaningful improvement in mood and anxiety is experienced. Antidepressants are prescription-only medicines; always obtained through a doctor, psychiatrist, or other licensed prescriber. They are approved by regulatory agencies including the FDA and EMA for specific psychiatric indications and are among the most prescribed classes of drugs worldwide.

Antidepressants are prescribed for a wide range of mental health and medical conditions. Primary on-label uses include major depressive disorder (MDD), generalized anxiety disorder (GAD), social anxiety disorder (social phobia), panic disorder, obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), and premenstrual dysphoric disorder (PMDD). SSRIs (fluoxetine, sertraline, escitalopram, citalopram, paroxetine) are first-line treatment for most of these conditions, recommended in clinical guidelines from NICE, APA, and WHO. SNRIs (venlafaxine, duloxetine) are also first-line and are particularly useful when comorbid pain is present. TCAs (amitriptyline, nortriptyline, clomipramine) are used in treatment-resistant depression, neuropathic pain, migraine prophylaxis, and OCD. MAOIs (phenelzine, tranylcypromine) are reserved for refractory depression. Off-label established uses include eating disorders (bulimia nervosa — fluoxetine), chronic pain syndromes (fibromyalgia, neuropathic pain — duloxetine, amitriptyline), hot flushes (venlafaxine, paroxetine), and premature ejaculation (SSRIs). Prescribers include psychiatrists, general practitioners, and specialist mental health nurses.

SSRIs (selective serotonin reuptake inhibitors) block the serotonin transporter (SERT) protein in the presynaptic neuron, which normally reabsorbs serotonin from the synaptic cleft back into the neuron. By inhibiting this reuptake process, SSRIs increase the availability of serotonin in the synapse, allowing it to continue acting on postsynaptic serotonin receptors and thereby enhancing serotonergic neurotransmission. This modulation of the serotonin system in brain regions including the prefrontal cortex, limbic system, and hippocampus underlies the antidepressant and anxiolytic effects. SNRIs (serotonin-norepinephrine reuptake inhibitors such as venlafaxine and duloxetine) do the same for both serotonin and norepinephrine, providing broader neurotransmitter modulation and additional benefit for pain pathways. Tricyclic antidepressants (TCAs) also inhibit serotonin and norepinephrine reuptake but additionally block muscarinic, histamine H1, and alpha-adrenergic receptors — which explains their significantly greater side effect burden. MAOIs irreversibly inhibit monoamine oxidase enzymes that break down serotonin, norepinephrine, and dopamine. All antidepressant classes require 4–6 weeks to achieve full therapeutic effect as neuroadaptive changes in receptor expression and downstream signaling develop gradually.

Antidepressant dosing is always individualized by the prescribing clinician based on the indication, patient tolerability, and clinical response. Treatment typically begins at a low starting dose and is gradually increased over weeks. Common starting and therapeutic doses: fluoxetine 20 mg/day (range 20–60 mg); sertraline 50 mg/day (range 50–200 mg); escitalopram 10 mg/day (range 10–20 mg); citalopram 20 mg/day (range 20–40 mg); paroxetine 20 mg/day (range 20–50 mg); venlafaxine 75 mg/day (range 75–375 mg); duloxetine 60 mg/day (range 30–120 mg); mirtazapine 15 mg at night (range 15–45 mg). TCAs (amitriptyline for depression): 10–25 mg at night, titrated to 75–150 mg. Most SSRIs and SNRIs are taken once daily, at a consistent time each day, with or without food. Liquid formulations are available for those who cannot swallow tablets (fluoxetine, sertraline). Never increase or decrease your dose without consulting your prescribing doctor.

Side effects vary between antidepressant classes and individual drugs. SSRIs and SNRIs commonly cause the following in the first 1–2 weeks (which often improve with continued treatment): nausea and upset stomach (20–30% of users), headache (15–20%), insomnia or excessive drowsiness, initial increased anxiety or agitation, and diarrhea or loose stools. Sexual dysfunction — including reduced libido (20–30%), delayed or absent orgasm, and erectile dysfunction — is a common and often persistent side effect, affecting more than 30% of SSRI users. Weight changes (gain most commonly with paroxetine and mirtazapine; occasional loss initially) occur with prolonged use. SSRIs and SNRIs may increase suicidal thoughts and behaviors in children, adolescents, and young adults (aged under 25) particularly during the first weeks of treatment or after dose increases — this requires close clinical monitoring and immediate reporting if it occurs. TCAs cause significantly more anticholinergic side effects (dry mouth, constipation, urinary retention, blurred vision, confusion in elderly) and are cardiotoxic in overdose — fatal in small excesses — making them unsuitable for patients at suicide risk. Mirtazapine commonly causes weight gain and sedation. Serotonin syndrome — characterized by agitation, tremor, hyperreflexia, diaphoresis, tachycardia, and hyperthermia — is a rare but potentially life-threatening reaction when two or more serotonergic drugs are combined, including tramadol, triptans, St. John's Wort, and linezolid.

Antidepressants carry an FDA and MHRA black-box warning for increased risk of suicidal thinking and behavior in children, adolescents, and young adults (under 25) during initial treatment weeks — close monitoring is mandatory in this age group, typically weekly for the first month. Never abruptly stop antidepressants — this causes discontinuation syndrome (also called antidepressant withdrawal), which can be severe and debilitating: symptoms include electric shock-like sensations ('brain zaps'), dizziness, nausea, flu-like symptoms, irritability, and rebound anxiety and depression. Antidepressants should always be tapered slowly under medical supervision when stopping — the taper may take weeks to months depending on the drug and duration of use. MAOIs have the most dangerous drug interaction profile of any antidepressant class: they can cause fatal hypertensive crises with tyramine-rich foods (aged cheese, cured meats, fermented products), and potentially fatal serotonin syndrome with other serotonergic drugs — a washout period of at least 14 days is required between MAOIs and other antidepressants. SSRIs reduce platelet aggregation and increase bleeding risk — particularly in combination with NSAIDs (ibuprofen, naproxen) or anticoagulants (warfarin); add a gastric protective agent (PPI) if combining. Escitalopram and citalopram at higher doses can prolong the QT interval — avoid in patients with pre-existing cardiac conditions or on other QT-prolonging drugs. SSRIs can cause hyponatremia (low blood sodium) particularly in elderly patients — monitor sodium in this group. Always inform all healthcare providers of your antidepressant use and never self-medicate psychiatric conditions.