Drug Therapy

Drug Therapy for Schizophrenia: Typical and Atypical Antipsychotics

Antipsychotic medication is the cornerstone of schizophrenia treatment. Two generations of antipsychotics have been developed, differing in their receptor profiles, efficacy for different symptom clusters, and side effect profiles.

Typical (First-Generation) Antipsychotics

The typical antipsychotics (also called first-generation or conventional antipsychotics) were developed from the 1950s. Examples include chlorpromazine (the first antipsychotic, discovered 1952) and haloperidol. Their primary mechanism of action is D2 receptor antagonism — they block dopamine D2 receptors, reducing mesolimbic dopamine transmission and thereby alleviating positive symptoms (hallucinations, delusions). They are broadly effective for positive symptoms in approximately 70% of patients.

Side effects are a major limitation. By blocking D2 receptors throughout the brain — including the nigrostriatal pathway (involved in motor control) — typical antipsychotics produce extrapyramidal side effects (EPS):

• Parkinsonism: tremor, rigidity, bradykinesia (slowed movement) — resembling Parkinson's disease.
• Akathisia: a distressing inner sense of restlessness and compulsion to move.
• Acute dystonia: involuntary muscle contractions, particularly of the face and neck.
• Tardive dyskinesia (TD): with long-term use, involuntary repetitive movements of the face, tongue, and limbs — sometimes irreversible. Prevalence: approximately 25–30% of long-term users.

Typical antipsychotics also block histamine (causing sedation) and muscarinic receptors (causing dry mouth, constipation, blurred vision).

Atypical (Second-Generation) Antipsychotics

The atypical antipsychotics (second-generation) were developed from the 1990s. Examples include clozapine, risperidone, olanzapine, and quetiapine. They differ from typicals in having a broader receptor profile: they block D2 receptors at lower affinity and additionally block serotonin 5-HT2A receptors, amongst others. This broader profile is associated with:

• Lower incidence of extrapyramidal side effects (because the D2 blockade is less pronounced in the nigrostriatal pathway)
• Possibly greater efficacy for negative symptoms and cognitive deficits (though evidence is modest)
• Clozapine specifically: superior efficacy for treatment-resistant schizophrenia — effective in approximately 30–50% of patients who fail other antipsychotics. Mechanism unknown but likely involves D4, 5-HT, and muscarinic receptor effects.

Atypical side effects: reduced EPS but significant metabolic effects — weight gain (particularly olanzapine and clozapine), diabetes, dyslipidaemia, and metabolic syndrome, contributing to the elevated cardiovascular risk in schizophrenia. Clozapine specifically carries risk of agranulocytosis (dangerous reduction in white blood cells) in approximately 1–2% of patients — requiring mandatory regular blood monitoring. Clozapine also causes sedation and hypersalivation.

Evaluation

Antipsychotics are the most effective available treatments for positive symptoms and have transformed the management of schizophrenia. However, 25–30% of patients show limited response; negative symptoms and cognitive deficits remain largely treatment-resistant; non-adherence (often due to side effects) is a major clinical problem; and long-term side effects (metabolic syndrome, TD) substantially impair quality of life. The development of more targeted and better-tolerated treatments remains an unmet clinical need.