PSYCHOPHARMACOLOGY
By Dr. Pius Wabas
Introduction
Psychopharmacology is the branch of science that studies the effects of drugs on mood,
behavior, cognition, and mental processes. It is a core aspect of psychiatry and clinical
psychology, as it explains how medications alter brain function to treat mental disorders.
The field combines principles from pharmacology, neuroscience, psychology, and medicine.
Psychopharmacology is essential because most psychiatric disorders involve imbalances in
neurotransmitters such as dopamine, serotonin, norepinephrine, acetylcholine, and gamma-
aminobutyric acid (GABA). By understanding these chemical messengers, clinicians can
prescribe appropriate medications to restore balance and improve functioning.
Basic Principles of Psychopharmacology
1. Pharmacokinetics – What the body does to the drug: absorption, distribution,
metabolism, excretion (ADME).
2. Pharmacodynamics – What the drug does to the body: mechanism of action, agonists vs
antagonists, dose-response relationship.
3. Therapeutic Window – Range between effective dose and toxic dose.
4. Tolerance and Dependence – Body adaptation to drugs, risk of withdrawal if
discontinued.
Major Classes of Psychotropic Medications
1. Antipsychotics
Mode of Action:
- Typical (First-Generation): Block dopamine D2 receptors in mesolimbic pathway → reduce
positive symptoms.
- Atypical (Second-Generation): Block both dopamine D2 and serotonin 5-HT2A receptors →
treat positive and negative symptoms.
Examples: Haloperidol, Chlorpromazine (typical); Risperidone, Olanzapine, Quetiapine,
Clozapine (atypical).
Extrapyramidal Side Effects (EPSE)
Acute Dystonia – sudden sustained muscle contractions (neck, jaw, eyes). Management:
anticholinergics.
, Akathisia – inner restlessness, inability to sit still. Management: propranolol,
benzodiazepines.
Parkinsonism – rigidity, tremor, shuffling gait. Management: anticholinergics,
amantadine.
Tardive Dyskinesia – repetitive involuntary movements, often irreversible.
Management: switch to atypicals, VMAT2 inhibitors.
Other Side Effects
Neuroleptic Malignant Syndrome (NMS): rigidity, hyperthermia, autonomic instability.
Metabolic Syndrome: weight gain, diabetes, dyslipidemia (common with olanzapine,
clozapine).
Anticholinergic Effects: dry mouth, constipation, blurred vision, urinary retention.
Orthostatic Hypotension due to alpha-1 blockade.
Sedation due to H1 receptor blockade.
Endocrine: Hyperprolactinemia (galactorrhea, gynecomastia, amenorrhea).
Agranulocytosis (clozapine). Requires regular blood monitoring.
2. Antidepressants
Mode of Action:
- SSRIs: Block serotonin reuptake.
- SNRIs: Block serotonin and norepinephrine reuptake.
- TCAs: Block serotonin and norepinephrine reuptake + antagonize muscarinic, histamine,
alpha-adrenergic receptors.
- MAOIs: Inhibit monoamine oxidase → ↑ serotonin, norepinephrine, dopamine.
Examples: SSRIs (Fluoxetine, Sertraline), SNRIs (Venlafaxine, Duloxetine), TCAs
(Amitriptyline, Imipramine), MAOIs (Phenelzine, Tranylcypromine).
3. Mood Stabilizers
Mode of Action:
- Lithium: Alters sodium transport, modulates G-proteins.
- Valproate: Increases GABA, blocks sodium channels.
- Carbamazepine: Blocks sodium channels.
- Lamotrigine: Inhibits glutamate release, blocks sodium channels.
Examples: Lithium, Valproate, Carbamazepine, Lamotrigine.
4. Anxiolytics
Mode of Action:
- Benzodiazepines: Bind to GABA-A receptor → increase Cl- channel opening frequency →
hyperpolarization.
- Buspirone: Partial agonist at 5-HT1A receptor.
Examples: Diazepam, Lorazepam, Buspirone.
By Dr. Pius Wabas
Introduction
Psychopharmacology is the branch of science that studies the effects of drugs on mood,
behavior, cognition, and mental processes. It is a core aspect of psychiatry and clinical
psychology, as it explains how medications alter brain function to treat mental disorders.
The field combines principles from pharmacology, neuroscience, psychology, and medicine.
Psychopharmacology is essential because most psychiatric disorders involve imbalances in
neurotransmitters such as dopamine, serotonin, norepinephrine, acetylcholine, and gamma-
aminobutyric acid (GABA). By understanding these chemical messengers, clinicians can
prescribe appropriate medications to restore balance and improve functioning.
Basic Principles of Psychopharmacology
1. Pharmacokinetics – What the body does to the drug: absorption, distribution,
metabolism, excretion (ADME).
2. Pharmacodynamics – What the drug does to the body: mechanism of action, agonists vs
antagonists, dose-response relationship.
3. Therapeutic Window – Range between effective dose and toxic dose.
4. Tolerance and Dependence – Body adaptation to drugs, risk of withdrawal if
discontinued.
Major Classes of Psychotropic Medications
1. Antipsychotics
Mode of Action:
- Typical (First-Generation): Block dopamine D2 receptors in mesolimbic pathway → reduce
positive symptoms.
- Atypical (Second-Generation): Block both dopamine D2 and serotonin 5-HT2A receptors →
treat positive and negative symptoms.
Examples: Haloperidol, Chlorpromazine (typical); Risperidone, Olanzapine, Quetiapine,
Clozapine (atypical).
Extrapyramidal Side Effects (EPSE)
Acute Dystonia – sudden sustained muscle contractions (neck, jaw, eyes). Management:
anticholinergics.
, Akathisia – inner restlessness, inability to sit still. Management: propranolol,
benzodiazepines.
Parkinsonism – rigidity, tremor, shuffling gait. Management: anticholinergics,
amantadine.
Tardive Dyskinesia – repetitive involuntary movements, often irreversible.
Management: switch to atypicals, VMAT2 inhibitors.
Other Side Effects
Neuroleptic Malignant Syndrome (NMS): rigidity, hyperthermia, autonomic instability.
Metabolic Syndrome: weight gain, diabetes, dyslipidemia (common with olanzapine,
clozapine).
Anticholinergic Effects: dry mouth, constipation, blurred vision, urinary retention.
Orthostatic Hypotension due to alpha-1 blockade.
Sedation due to H1 receptor blockade.
Endocrine: Hyperprolactinemia (galactorrhea, gynecomastia, amenorrhea).
Agranulocytosis (clozapine). Requires regular blood monitoring.
2. Antidepressants
Mode of Action:
- SSRIs: Block serotonin reuptake.
- SNRIs: Block serotonin and norepinephrine reuptake.
- TCAs: Block serotonin and norepinephrine reuptake + antagonize muscarinic, histamine,
alpha-adrenergic receptors.
- MAOIs: Inhibit monoamine oxidase → ↑ serotonin, norepinephrine, dopamine.
Examples: SSRIs (Fluoxetine, Sertraline), SNRIs (Venlafaxine, Duloxetine), TCAs
(Amitriptyline, Imipramine), MAOIs (Phenelzine, Tranylcypromine).
3. Mood Stabilizers
Mode of Action:
- Lithium: Alters sodium transport, modulates G-proteins.
- Valproate: Increases GABA, blocks sodium channels.
- Carbamazepine: Blocks sodium channels.
- Lamotrigine: Inhibits glutamate release, blocks sodium channels.
Examples: Lithium, Valproate, Carbamazepine, Lamotrigine.
4. Anxiolytics
Mode of Action:
- Benzodiazepines: Bind to GABA-A receptor → increase Cl- channel opening frequency →
hyperpolarization.
- Buspirone: Partial agonist at 5-HT1A receptor.
Examples: Diazepam, Lorazepam, Buspirone.
