Psychiatric medications are effective treatments for a wide range of mental disorders. Understanding their mechanisms, indications, side effects, and monitoring requirements is essential for safe and effective use.

Brain and medication — Psychiatric medications are central to the treatment of mental health disorders, acting on neurotransmitter systems to alleviate symptoms. Source: Unsplash.

Antidepressants

Brain mindfulness — Antidepressants are among the most commonly prescribed psychiatric medications, with SSRIs and SNRIs as first-line treatments for depression and anxiety. Source: Unsplash.

SSRIs (Selective Serotonin Reuptake Inhibitors)

Mechanism: block the serotonin transporter (SERT), increasing synaptic serotonin. Common SSRIs: fluoxetine, escitalopram, sertraline, paroxetine, citalopram, and fluvoxamine. Indications: major depressive disorder, all anxiety disorders (GAD, panic, social anxiety, PTSD, OCD), bulimia nervosa (fluoxetine), and premenstrual dysphoric disorder.

Onset of therapeutic effect: 2–4 weeks (though some improvement may begin at 1–2 weeks). Full response: 6–12 weeks. Side effects: nausea (transient), headache, insomnia or sedation, sexual dysfunction (decreased libido, delayed ejaculation, anorgasmia — affecting 30–60%), weight gain (variable), and serotonin syndrome (rare, potentially fatal, caused by excess serotonin — features: confusion, agitation, hyperthermia, clonus, hyperreflexia, diarrhea).

SNRIs (Serotonin-Norepinephrine Reuptake Inhibitors)

Mechanism: block both SERT and NET. Examples: venlafaxine, duloxetine, desvenlafaxine, levomilnacipran. Indications: depression, GAD, panic disorder, and chronic pain conditions (duloxetine approved for fibromyalgia, diabetic neuropathy, musculoskeletal pain).

Atypical Antidepressants

Bupropion. Mechanism: inhibits reuptake of norepinephrine and dopamine (NDRI). Indications: depression, seasonal affective disorder, smoking cessation. Advantage: minimal sexual dysfunction, activating properties (useful for fatigue, anergia). Contraindicated in seizure disorders, eating disorders.

Mirtazapine. Mechanism: antagonist at alpha-2, 5-HT2, and H1 receptors. Indications: depression. Advantages: sedation (useful for insomnia), appetite stimulation (useful in depression with weight loss). Side effect: weight gain.

Trazodone. Primarily used for insomnia at low doses; antidepressant at higher doses. 5-HT2 antagonist and SERT inhibitor. Risk of priapism (rare but requires emergency treatment).

MAOIs (Monoamine Oxidase Inhibitors)

Mechanism: inhibit MAO-A and MAO-B, preventing breakdown of monoamines. Examples: phenelzine, tranylcypromine, isocarboxazid. Indications: treatment-resistant depression, atypical depression, panic. Dietary restrictions: avoid tyramine-rich foods (aged cheese, cured meats, fermented foods, soy sauce, tap beer) to prevent hypertensive crisis. Medication interactions: multiple. MAOIs are last-line due to safety requirements but highly effective for refractory cases.

ⓘ Information

Antidepressant discontinuation syndrome occurs with abrupt cessation, particularly with SSRIs with short half-lives (paroxetine, venlafaxine). Symptoms: dizziness, nausea, headache, sensory disturbances (electric shock sensations), anxiety, insomnia, and irritability. Prevention: gradual taper over weeks to months. Distinguishing discontinuation from relapse: discontinuation symptoms begin within days, are transient (1–3 weeks), and include somatic symptoms not typical of the original disorder. Switching antidepressants requires consideration of washout periods to avoid serotonin syndrome (especially when switching from MAOIs).

Antipsychotics

First-Generation (Typical) Antipsychotics

Mechanism: D2 dopamine receptor blockade. Examples: haloperidol, chlorpromazine, fluphenazine, perphenazine, thiothixene. Indications: schizophrenia, acute mania, agitation, Tourette syndrome. Side effects: extrapyramidal symptoms (acute dystonia, parkinsonism — tremor, rigidity, bradykinesia, akathisia — inner restlessness, pacing), tardive dyskinesia (involuntary orofacial and extremity movements, potentially irreversible, highest risk with long-term use), neuroleptic malignant syndrome (rigidity, fever, autonomic instability, elevated CK — medical emergency), and prolactin elevation (galactorrhea, gynecomastia, sexual dysfunction).

Second-Generation (Atypical) Antipsychotics

Mechanism: D2 and 5-HT2A antagonism. Examples: clozapine, risperidone, olanzapine, quetiapine, aripiprazole, ziprasidone, paliperidone, lurasidone, iloperidone, asenapine, brexpiprazole, cariprazine. Second-generation antipsychotics cause fewer extrapyramidal symptoms but significant metabolic side effects: weight gain, hyperglycemia, diabetes mellitus, and dyslipidemia. These side effects require baseline and regular monitoring of weight, BMI, fasting glucose, and lipids.

Clozapine is uniquely effective for treatment-resistant schizophrenia and reduces suicidality. It requires mandatory blood monitoring for agranulocytosis (absolute neutrophil count every week for first 6 months, then every 2 weeks for 6 months, then monthly). Other side effects: myocarditis, seizures, sedation, sialorrhea, and metabolic syndrome.

Mood Stabilizers

Lithium. Mechanism: multiple (inhibits inositol monophosphatase, GSK-3 beta, modulates neurotransmitters). Gold standard for bipolar I disorder — reduces mania, depression, and suicide risk by 60%. Narrow therapeutic index (0.6–1.2 mEq/L). Toxicity: tremor, nausea, diarrhea, polyuria, polydipsia, hypothyroidism, renal impairment (nephrogenic diabetes insipidus, chronic kidney disease). Monitoring: lithium level every 3–6 months (more frequently during dose changes), renal function, thyroid function, and calcium.

Valproate (valproic acid, divalproex). Indications: acute mania, bipolar maintenance, epilepsy. Side effects: weight gain, tremor, sedation, hepatotoxicity, thrombocytopenia, polycystic ovary syndrome. Fetal risks: neural tube defects (teratogenic).

Lamotrigine. Indications: bipolar depression and maintenance (more effective for preventing depression than mania). Slow titration required due to risk of Stevens-Johnson syndrome (severe, potentially fatal rash — risk 0.08–0.3%). Discontinue if any rash appears.

Carbamazepine. Indications: acute mania (especially in rapid cycling), epilepsy. Side effects: dizziness, ataxia, diplopia, hyponatremia, agranulocytosis, aplastic anemia. Strong CYP3A4 inducer — numerous drug interactions.

Anxiolytics

Benzodiazepines. GABA-A positive allosteric modulators. Short-acting: alprazolam, lorazepam, triazolam. Long-acting: clonazepam, diazepam, chlordiazepoxide. Indications: acute anxiety, panic disorder, alcohol withdrawal, catatonia, seizure disorders. Risks: sedation, cognitive impairment, ataxia (falls risk in elderly), tolerance and dependence (tolerance develops in weeks to months), withdrawal syndrome (anxiety, insomnia, seizures, delirium — can be life-threatening). Tolerance and dependence limit use to short-term or intermittent treatment. Discontinuation requires slow taper over weeks to months.

Non-benzodiazepine anxiolytics: buspirone (5-HT1A partial agonist, minimal abuse potential, delayed onset of 2–4 weeks), pregabalin and gabapentin (calcium channel alpha-2-delta ligands, approved for fibromyalgia and neuropathic pain, used for GAD), and hydroxyzine (H1 antihistamine).

Stimulants

Mechanism: inhibit DAT and NET, increasing dopamine and norepinephrine. Methylphenidate and amphetamine derivatives (dextroamphetamine, mixed amphetamine salts, lisdexamfetamine). Indications: ADHD (first-line), narcolepsy. Side effects: decreased appetite, insomnia, headache, stomachache, irritability, anxiety, tics, and (rarely) cardiovascular effects (blood pressure and heart rate elevation). Growth monitoring in children. Misuse potential requires prescribing controls.

⚠ Clinical Correlation

Genetic variation affects drug metabolism and response. CYP2D6 (metabolizes many antidepressants and antipsychotics) is highly polymorphic — poor metabolizers have higher drug levels and more side effects; ultrarapid metabolizers may have no response at standard doses. CYP2C19 (metabolizes escitalopram, sertraline, citalopram) and HLA-B*1502 (associated with carbamazepine-induced Stevens-Johnson syndrome in Asian populations) are clinically relevant. Pharmacogenetic testing can guide medication selection and dosing, particularly after failed trials. However, it explains only a minority of variation in treatment response, and clinical factors (severity, adherence, comorbidities) remain paramount.

Summary

Psychiatric medications target neurotransmitter systems (serotonin, dopamine, norepinephrine, GABA, glutamate) to reduce symptoms of mental disorders. SSRIs and SNRIs are first-line antidepressants. Second-generation antipsychotics are first-line for schizophrenia but require metabolic monitoring. Lithium is the gold standard mood stabilizer. Benzodiazepines are effective short-term but carry addiction risk. Stimulants are first-line for ADHD. Medication selection considers diagnosis, symptom profile, side effect profile, patient preference, and pharmacogenetic factors. Combination with psychotherapy produces superior outcomes for most disorders.