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Extrapyramidal side effects matter because they follow a predictable timeline after starting a dopamine-blocking drug, and knowing that timeline helps tell apart two look-alike movement problems, acute dystoniaInvoluntary muscle contractions causing abnormal, sometimes painful, postures or movements.Read more → and drug-induced parkinsonism. Both arise from D2 receptorThe main dopamine receptor subtype that antipsychotic drugs block to reduce psychotic symptoms.Read more → (a dopamine receptor subtype) blockade in the nigrostriatal pathwayA dopamine brain pathway that controls movement, whose blockade by antipsychotics causes Parkinson's-like side effects.Read more →, a brain circuit that normally coordinates smooth movement. Acute dystonia appears within hours to days and causes sudden, sustained muscle spasms. Drug-induced parkinsonism instead appears over days to weeks and causes slowness, stiffness and tremor resembling Parkinson's disease. For example, imagine a patient started on haloperidol yesterday who now has their neck twisted to one side (torticollis): the rapid onset points to acute dystonia, not parkinsonism, even though both come from the same drug class.

D2 receptorThe main dopamine receptor subtype that antipsychotic drugs block to reduce psychotic symptoms.Read more → blockade in the nigrostriatal pathwayA dopamine brain pathway that controls movement, whose blockade by antipsychotics causes Parkinson's-like side effects.Read more → disrupts the normal balance between dopamine and acetylcholine that controls smooth movement. Acute dystoniaInvoluntary muscle contractions causing abnormal, sometimes painful, postures or movements.Read more → presents with sudden spasms, a stiff or twisted neck (torticollis), or an oculogyric crisis, where the eyes roll upward involuntarily, and is treated with an anticholinergicBlocking the action of acetylcholine, a nerve chemical, causing effects like a dry mouth and blurred vision.Read more → drug such as procyclidine, which restores the balance quickly. Drug-induced parkinsonism instead presents more gradually, over days to weeks, with bradykinesia (slowness of movement), rigidity and a tremor, closely mimicking Parkinson's disease itself. For example, imagine a patient on haloperidol for three weeks who has developed a shuffling gait and reduced arm swing: this gradual pattern points to parkinsonism rather than dystonia. In practice, this means both conditions are managed by reducing the causative drug or adding an anticholinergic, but recognising which one is present guides how urgently treatment is needed.

• A registrar must distinguish drug-induced parkinsonism from idiopathic Parkinson's disease in a woman on an antipsychotic. Which feature most favours the drug-induced cause?
• An antipsychotic causing parkinsonism is withdrawn in an elderly man. How long should the team expect the movement signs to take to settle after stopping?
• A young woman given a drug for nausea after surgery develops a sustained painful neck spasm. Which prescribed drug most likely caused this movement reaction?
• A trainee proposes prescribing procyclidine routinely alongside every new antipsychotic. Which argument against routine prophylaxis of this kind is strongest?

• Acute dystonia, sudden sustained spasms within hours to days, unlike drug-induced parkinsonism's gradual onset over days to weeks.
• Drug-induced parkinsonism, bradykinesia, rigidity and tremor resembling Parkinson's disease, rather than the sudden spasms of acute dystoniaInvoluntary muscle contractions causing abnormal, sometimes painful, postures or movements.Read more →.
• Akathisia, a subjective inner restlessness with an urge to move, unlike the involuntary sustained spasms of dystoniaInvoluntary muscle contractions causing abnormal, sometimes painful, postures or movements.Read more → or the slowness of parkinsonism.
• Tardive dyskinesia, a late, months-to-years complication with involuntary orofacial movements, whereas dystoniaInvoluntary muscle contractions causing abnormal, sometimes painful, postures or movements.Read more → and parkinsonism appear early and anticholinergicsDrugs that block the action of acetylcholine, a nerve chemical, causing effects like a dry mouth and blurred vision.Read more → worsen tardive dyskinesia rather than helping it.

• Persistence beyond five years suggests a different underlying illness.
• That antihistamine antiemetic is not a typical cause of this reaction.
• One-sided signs evolving slowly are typical of the degenerative illness.
• A marked one-sided resting tremor favours the degenerative illness.
• Early loss of smell is characteristic of the degenerative illness.

• Identify the drug, receptor, enzyme or pharmacokinetic change named in the stem.
• Translate it into the immediate mechanism before looking at the options.
• Use timing and the adverse-effect pattern to separate the nearest alternatives.
• Check whether the question asks for mechanism, clinical consequence, monitoring or management.