Adjunctive Metformin for Antipsychotic-induced Hyperprolactinemia: A Systematic Review

This systematic review examines adjunctive metformin therapy for the treatment of antipsychotic-induced hyperprolactinemia. A computerized search of databases in Chinese and the international databases in English provided three trials with a total of 325 patients including one randomized clinical trial (RCT) and two observational studies (single-group, before-after design). A meta-analysis could not be conducted. The quality of evidence ranged from "very low" to "moderate". Metformin patients had a significant decrease in serum prolactin level with a mean of 54.6μg/l in the three trials. In the RCT, menstruation restarted in 67% of those with menstrual disturbances versus 5% in placebo. In one observational study, 91% of patients no longer had signs or symptoms of galactorrhea. In the RCT, adverse drug reactions (ADRs) occurred at similar incidence rates among metformin and placebo patients, except that no significant increases in nausea, insomnia and agitation occurred which were not associated with discontinuations. Our systematic review indicated that adjunctive metformin significantly lowered prolactin level and relieved prolactin-related symptoms in patients with antipsychotic-induced hyperprolactinemia. Future higher quality RCTs need to verify the currently available limited evidence based on three trials which suggest that adjunctive metformin may be used effectively and safely for antipsychotic-induced hyperprolactinemia.