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3.10 Antimuscarinic adverse effects

Antimuscarinic1 effects include nasal stuffiness, dry mouth, impaired intestinal peristalsis (and a tendency to constipation and even obstruction—see also under Gastrointestinal adverse effects), and urinary retention. For antimuscarinic effects on the eye, see under Adverse effects on the eye.

Antipsychotics vary in their capacity to block acetylcholine receptors (see Classification of antipsychotic) and thereby to produce antimuscarinic (anticholinergic) side effects.

Factors which increase risk

The risk of harm from antimuscarinic effects is increased in patients with myasthenia gravis, and prostatic hypertrophy.

Concomitant use of an antimuscarinic drug with an antipsychotic might increase the risk of antimuscarinic effects and hypotension.

Risk-reduction measures

Initiating treatment with a low dose of an antipsychotic can help to avoid excessive antimuscarinic effects; the dose can be increased as tolerance develops.

This learning module discusses noteworthy risks for antipsychotics. Summaries of product characteristics and the BNF should be consulted for a fuller account of the adverse effects and warnings for individual antipsychotics.

  1. Reduction or blocking of the effects of parasympathetic nerves; antimuscarinic effects include dry mouth, difficulty swallowing, blurred vision, confusion, palpitations, constipation, and urine retention