• Adverse effects of the atypical antipsychotics include weight gain, dizziness, and postural hypotension (especially during initial dose titration) which may be associated with syncope or reflex tachycardia in some people.
• Extrapyramidal symptoms may occur. These are usually mild and transient, and may respond to dose reduction or to an antimuscarinic drug (e.g. procyclidine).
• Tardive dyskinesia can occur on long-term administration. The drug should be discontinued on appearance of early signs.
• Risperidone can cause elevated prolactin levels.
• Hyperglycaemia, and sometimes diabetes, can occur, particularly with clozapine and olanzapine; monitoring weight and plasma glucose may identify the development of hyperglycaemia.
• Atypical antipsychotics may affect performance of skilled tasks (e.g. driving); effects of alcohol are enhanced.
• Olanzapine and risperidone are associated with an increased risk of stroke in elderly people with dementia. The Committee on Safety of Medicines has advised [CSM, 2004] that:
• Risperidone or olanzapine should not be used for treating behavioural symptoms of dementia.
• For acute psychotic conditions in elderly people with dementia, risperidone should be limited to short-term use under specialist advice; olanzapine is not licensed for acute psychosis.
• The possibility of cerebrovascular events should be considered carefully before treating people with a history of stroke or transient ischaemic attack; risk factors for cerebrovascular disease (e.g. hypertension, diabetes, smoking, and atrial fibrillation) should also be considered.

[BNF 56, 2008]