Weight change over two years in people prescribed olanzapine, quetiapine and risperidone in UK primary care: Cohort study in THIN, a UK primary care database.

BACKGROUND: Follow-up studies of weight gain related to antipsychotic treatment beyond a year are limited in number. We compared weight change in the three most commonly prescribed antipsychotics in a representative UK General Practice database.
METHOD: We conducted a cohort study in United Kingdom primary care records of people newly prescribed olanzapine, quetiapine or risperidone. The primary outcome was weight in each six month period for two years after treatment initiation. Weight changes were compared using linear regression, adjusted for age, baseline weight and diagnosis.
RESULTS: N = 6338 people received olanzapine, 12,984 quetiapine and 6556 risperidone. Baseline weight was lowest for men treated with olanzapine (80.8 kg versus 83.5 kg quetiapine, 82.0 kg risperidone) and women treated with olanzapine (67.7 kg versus 71.5 kg quetiapine 68.4 kg risperidone. Weight gain occurred during treatment with all three drugs. Compared with risperidone mean weight gain was higher with olanzapine (adjusted co-efficient +1.24 kg (95% confidence interval: 0.69-1.79 kg per six months) for men and +0.77 kg (95% confidence interval: 0.29-1.24 kg) for women). Weight gain with quetiapine was lower in unadjusted models compared with risperidone, but this difference was not significant after adjustment.
CONCLUSION: Olanzapine is more commonly prescribed to people with lower weight. However, after accounting for baseline weight, age, sex and diagnosis, olanzapine is still associated with greater weight gain over two years than risperidone or quetiapine. Baseline weight does not ameliorate the risks of weight gain associated with antipsychotic medication. Weight gain should be assertively discussed and managed for people prescribed antipsychotics, especially olanzapine.