Patients taking antipsychotic drugs could be at risk of venous thromboembolism, research published in the British Medical Journal suggests.

The study found that individuals prescribed with atypical antipsychotics in the previous two years had a more than 32% greater risk of developing a blood clot than non-users.

Patients taking quetiapine and low potency antipsychotics such as chlorpromazine, clozapine and thioridazine were found to be at the highest risk.

The research also showed that patients who had started a new drug in the previous three months had about twice the risk of venous thromboembolism.

More than 25,000 patients with deep vein thrombosis or a pulmonary embolism and 90,000 control patients took part in the study between January 1996 and July 2007. Each patient was matched with up to four controls by age, calendar time, sex, and practice.

Most antipsychotics used were conventional agents and were found to be associated with enhanced aggregation of platelets.