Antipsychotics learning module Extrapyramidal side effects: acute dystonia

Acute dystonia occurs relatively frequently with antipsychotic use. Dystonic reactions typically occur within the first few days of treatment and usually rapidly (eg within one hour) after a dose of an antipsychotic. Often the first symptom is a subjective feeling of distress followed by sustained contraction or repetitive movement of the affected muscles. Acute dystonias can manifest as facial grimacing, torticollis, oculogyric crisis, or other abnormal posturing. Dystonia of the tongue may cause a subjective sensation of ‘swollen tongue’ despite normal tongue size.

As well as being extremely distressing for the patient (and to those attending the patient), rarely, dystonias can have serious and even fatal consequences, particularly if pharyngeal, laryngeal and other muscles involved in breathing are affected.

Factors which increase risk

Acute dystonias are more likely with high-potency first-generation antipsychotics. Other risk factors include male gender, younger age (especially younger adults and children), no previous exposure to an antipsychotic, rapid dose escalation and abrupt discontinuation of antipsychotic treatment. Use of cocaine probably also increases the risk of acute dystonia.

Risk-reduction measures

It is best to start with a low dose of antipsychotic and increase it slowly to the minimum clinically effective dose, taking particular care with patients who have not previously received an antipsychotic.

Routine prescription of antimuscarinics to prevent antipsychotic-induced dystonias is not recommended, but an antimuscarinic can be considered if the antipsychotic is being given by intramuscular injection in an emergency or if an antipsychotic is being used in circumstances which pose high risk of acute dystonia.


Acute dystonias respond readily to antimuscarinic (anticholinergic) medicines such as orphenadrine, procyclidine or trihexyphenidyl (former name benzhexol). For more severe and life-threatening cases of dystonia, it may be necessary to give the antimuscarinic medicine intravenously; procyclidine can be injected intramuscularly or intravenously.

Did you know...

Young adults and children are at higher risk of acute dystonia, including oculogyric crisis and opisthotonos. The antiemetic metoclopramide is an antagonist at the dopamine D2 receptor. Great care is required if metoclopramide is given concurrently with an antipsychotic such as a phenothiazine because the combination increases the risk of extrapyramidal side effects.


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Page last modified: 03 October 2018