Weight gain is a common side effect of antipsychotic and antidepressive drug therapy, difficult both to avoid and to treat. In several randomized controlled studies, add-on treatment with metformin has been demonstrated to reduce olanzapine-induced weight gain. In our department of psychiatry and psychotherapy, metformin has been used against antihistaminic-drug-induced weight gain since 2008.

Primary: To demonstrate the efficacy of metformin for prophylaxis of antihistaminic-drug-induced weight gain in a cohort of psychiatric in-patients under naturalistic conditions. Secondary: To identify side-effects of add-on metformin therapy in non-diabetic psychiatric in-patients.

Retrospective case-control analysis of in-patient charts from 3400 psychiatric therapies between 2008 and 2010 at Ulm University Department of Psychiatry and Psychotherapy III. Cases were identified on the basis of metformin prescription without a diagnosis of diabetes. Controls were matched for gender, age, BMI, diagnosis, and drug treatment. Evaluation will be performed with descriptive statistics, covariance analyses and mixed models.

No serious side effects could be attributed to metformin therapy on the basis of the charts reviewed. Further results will be presented at the meeting.

Metformin appears to be safe with regard to side effects in psychiatric in-patients taking anti-histaminic drugs.