Antipsychotics & Antidepressants: Psychiatry Drugs Guide

Antipsychotics calm the hallucinations, delusions and disorganised thinking of psychosis mainly by blocking dopamine D2 receptors in the brain, while antidepressants lift persistent low mood by increasing the availability of serotonin and noradrenaline at nerve synapses. Anxiolytics such as benzodiazepines reduce acute anxiety by strengthening the calming effect of the neurotransmitter GABA. All three groups adjust brain signalling rather than sedating the person into silence.

This matters because schizophrenia, bipolar disorder and major depression are among the leading causes of disability worldwide, and they respond to medicines that took decades to develop.

Key Concepts

• Dopamine D2 blockade: the core action of every antipsychotic; it quiets psychotic symptoms but can also cause movement side effects.
• Typical antipsychotics: older drugs like haloperidol and chlorpromazine; strong D2 blockade, higher risk of movement disorders.
• Atypical antipsychotics: newer drugs like risperidone, olanzapine, quetiapine and aripiprazole; block D2 plus serotonin receptors, with lower movement risk but higher metabolic risk (weight gain, diabetes).
• Extrapyramidal symptoms (EPS): drug-induced movement problems: acute dystonia, parkinsonism, akathisia (restlessness) and tardive dyskinesia (late, sometimes permanent involuntary movements).
• Clozapine: the most effective antipsychotic for treatment-resistant schizophrenia, but it can cause agranulocytosis (loss of white blood cells), so regular blood counts are mandatory.
• SSRIs and SNRIs: selective serotonin reuptake inhibitors (fluoxetine, sertraline, escitalopram) and serotonin-noradrenaline reuptake inhibitors (venlafaxine, duloxetine); first-line for depression and anxiety.
• Serotonin syndrome: a toxic excess of serotonin (confusion, sweating, tremor, muscle clonus, fever), classically from combining an SSRI with an MAOI.

Formulas

• Time to steady state: approximately 5 half-lives. A drug taken daily reaches its full stable blood level after about 5 times its half-life.
• Washout before an MAOI: most SSRIs need about 5 half-lives cleared; fluoxetine, with its long-lasting metabolite, needs roughly a 5-week gap before an MAOI can be started safely.

Worked Example

Sertraline has a half-life of about 26 hours and is started at 50 mg daily for depression. Step 1: time to steady state = 5 times 26 hours = 130 hours. Step 2: 130 divided by 24 = 5.4 days. So the blood level stabilises after roughly five and a half days, yet the mood benefit still takes 2 to 4 weeks because the brain needs time to adapt its receptors. This arithmetic explains the standard counselling point: the drug is working in the blood within a week, but the mind catches up later, so the patient must not stop at day 10 thinking it has failed.

Common Misconceptions

• "Antidepressants should work in a few days." Sleep and appetite may improve in the first week, but real mood lift needs 2 to 4 weeks of continuous treatment as downstream brain changes develop.
• "Psychiatric drugs are addictive, so I will stop once I feel better." Antipsychotics and antidepressants are not addictive, but stopping early invites relapse; most guidelines advise continuing 6 to 12 months after a first depressive episode recovers.
• "Newer antipsychotics have no side effects." Atypicals trade movement problems for metabolic ones: significant weight gain, raised blood sugar and lipids. Weight, waist, blood pressure, glucose and lipids need regular checks.

Real-World Applications

• Schizophrenia and acute mania, where antipsychotics control psychosis and agitation.
• Major depressive disorder, where SSRIs and SNRIs are first-line treatment.
• Obsessive-compulsive disorder, panic disorder and generalised anxiety disorder, which respond to higher SSRI doses.
• Treatment-resistant schizophrenia, where clozapine succeeds after two other antipsychotics fail.

Antipsychotics quiet psychosis through dopamine blockade, antidepressants restore mood through serotonin and noradrenaline, and anxiolytics calm acute anxiety through GABA. Benefits build over weeks, side effects differ sharply between old and new drugs, and stopping early is the commonest reason treatment fails.