Antipsychotic drug use and risk of first-time idiopathic venous thromboembolism: a case-control study

Background Antipsychotic drugs have been associated with an increased risk of adverse events such as venous thromboembolism. Our aim was to assess this risk in users of conventional antipsychotic drugs who had been diagnosed with first-time, idiopathic venous thromboembolism. Methods From a baseline population of 29 952 recipients of conventional and atypical antipsychotic drugs aged younger than 60 years, we identified 42 individuals with idiopathic venous thromboembolism and 172 matched controls. We compared risk of current and recent use of antipsychotic drugs with non-use before the index date in cases and controls. Findings Current exposure to conventional antipsychotic drugs was associated with a significantly increased risk of idiopathic venous thromboembolism compared with non-use (adjusted odds ratio 7·1 [95% CI 2·3–21·97]). Although we found no difference between phenothiazines, thioxanthenes, or other conventional antipsychotic drugs, low potency antipsychotic drugs drugs such as chlorpromazine and thioridazine were more strongly associated with venous thromboembolism (odds ratio 24·1 [3·3–172·7]) than were high potency antipsychotic drugs such as haloperidol (3·3 [0·8–13·2]). The risk for venous thrombosis was highest during the first few months of conventional antipsychotic drug use. Interpretation Current exposure to conventional antipsychotic drugs significantly increases the risk of idiopathic venous thromboembolism in men and women younger than 60 years of age.