25. PSYCHOTROPIC DRUGS

Introduction

Psychotropic drugs are medicines that act on the brain and alter mental functions such as mood, behaviour, perception and thinking. They are widely used in psychiatric conditions like depression, anxiety, schizophrenia, bipolar disorder and sleep disturbances. Major groups include antidepressants, anti-anxiety drugs, antipsychotics, mood stabilizers and central nervous system (CNS) stimulants.

1. Antidepressants

Antidepressants are used to treat different types of depression such as reactive depression, endogenous depression and depression associated with anxiety. They improve mood by increasing the levels of neurotransmitters like norepinephrine (NE), serotonin (5-HT) and dopamine (DA) in the brain.

Classification

  • Tricyclic antidepressants (TCAs): Imipramine, Amitriptyline, Clomipramine
  • SNRIs: Venlafaxine, Duloxetine
  • Norepinephrine reuptake inhibitors: Desipramine, Maprotiline
  • SSRIs: Fluoxetine, Sertraline, Citalopram, Paroxetine
  • Atypical antidepressants: Trazodone, Mirtazapine, Bupropion
  • MAO inhibitors: Tranylcypromine, Moclobemide
  • Herbal: St. John’s wort

Mechanism of Action

Most antidepressants work by blocking the reuptake of NE and 5-HT into nerve terminals, increasing their concentration at receptors. SSRIs selectively increase serotonin levels, while MAO inhibitors prevent the breakdown of brain amines. Atypical antidepressants act through multiple pathways like blocking 5-HT2 receptors or increasing release of NE.

Uses

  • Treatment of depression (all types)
  • Panic disorder, social phobia and OCD (SSRIs preferred)
  • Chronic neuropathic pain (TCAs)
  • Bed-wetting in children (Imipramine)
  • Migraine prevention (Amitriptyline)
  • Bulimia (Fluoxetine)
  • Smoking cessation (Bupropion)

Adverse Effects

  • TCAs: sedation, constipation, urinary retention, postural hypotension, arrhythmias
  • SSRIs: nausea, insomnia, sexual dysfunction
  • SNRIs: headache, withdrawal symptoms
  • MAO inhibitors: weight gain, hypotension, food interactions (tyramine crisis)
  • Atypical antidepressants: sedation (mirtazapine), priapism (trazodone)

2. Anti-Anxiety Drugs (Anxiolytics)

These drugs reduce tension, fear and excessive worry. They are useful in anxiety disorders, panic disorders and related conditions.

Main Drugs

  • Benzodiazepines: Diazepam, Lorazepam, Alprazolam (fast relief, short-term use)
  • Buspirone: Non-sedating, no dependence, useful in generalized anxiety
  • Beta blockers: Propranolol for physical symptoms like tremors
  • SSRIs/SNRIs: For long-term anxiety disorders
  • Hydroxyzine: Sedative antihistamine with anxiolytic effect

Side Effects

Benzodiazepines may cause drowsiness, memory problems and dependence. Buspirone has slow onset and may cause headache or dizziness.

3. CNS Stimulants

CNS stimulants increase alertness, motor activity, concentration and reduce fatigue. They are mainly used in ADHD and narcolepsy.

Types

  • Amphetamine group: Amphetamine, Methylphenidate, MDMA
  • Non-amphetamine: Modafinil, Atomoxetine
  • Methylxanthines: Caffeine, Theophylline

Mechanism

Amphetamines release dopamine and norepinephrine in synapses. Methylxanthines inhibit phosphodiesterase and block adenosine receptors, leading to CNS stimulation and bronchodilation.

Uses

  • ADHD (Methylphenidate, Atomoxetine)
  • Narcolepsy (Modafinil)
  • Migraine (Caffeine combinations)
  • Asthma (Theophylline)

Adverse Effects

  • Insomnia, irritability, hypertension
  • Dependence and withdrawal (amphetamines)
  • Theophylline toxicity: palpitations, seizures

4. Antipsychotic Drugs

Antipsychotics are used to treat schizophrenia and psychotic disorders. They control hallucinations, delusions and abnormal behaviour.

Classification

  • Typical antipsychotics: Chlorpromazine, Haloperidol, Trifluoperazine
  • Atypical antipsychotics: Clozapine, Risperidone, Olanzapine, Quetiapine

Mechanism

Typical antipsychotics block dopamine D2 receptors. Atypical antipsychotics block both 5-HT2A and D2 receptors, leading to fewer movement-related side effects.

Uses

  • Schizophrenia and schizoaffective disorders
  • Drug-induced psychosis
  • Severe agitation
  • Tourette’s syndrome
  • Hiccups (Chlorpromazine)
  • Antiemetic effect (Prochlorperazine)

Adverse Effects

  • Sedation and weight gain
  • Movement disorders: dystonia, akathisia, parkinsonism, tardive dyskinesia
  • Neuroleptic malignant syndrome
  • Hormonal effects: galactorrhoea, gynaecomastia
  • Hypotension

5. Mood Stabilizers

Mood stabilizers are used in bipolar disorder to control manic and depressive episodes.

Main Drugs

  • Lithium: Classic mood stabilizer
  • Valproate: First choice for acute mania
  • Carbamazepine: Useful in bipolar disorder
  • Atypical antipsychotics: Risperidone, Olanzapine
  • Lamotrigine: For bipolar depression prophylaxis

Lithium

Lithium reduces manic excitement and stabilizes mood. It is excreted by kidneys and has a narrow safety range (0.5–1.5 mEq/L). Monitoring is required.

Adverse Effects

  • Tremors, nausea, diarrhea
  • Hypothyroidism
  • Weight gain and edema
  • Kidney problems (nephrogenic diabetes insipidus)
  • Toxicity with sodium depletion

Detailed Notes:

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