Abstract
Metformin, a biguanide drug, is emerging as an important treatment option for the prevention or treatment of weight gain, type 2 diabetes mellitus, and the metabolic syndrome in psychiatric patients, especially those who require or receive antipsychotic drugs. Metformin treatment is commonly associated with gastrointestinal adverse effects; the risk of these is reduced by gradual dose uptitration, administration of the drug with meals, and use of a time-release formulation. Lactic acidosis, a potentially fatal complication of biguanide therapy, is very rare with metformin; the risk can be reduced by avoidance of its prescription in patients with impaired renal function, impaired liver function, cardiac failure, and certain other conditions. Long-term metformin use is associated with decreased vitamin B₁₂ levels, and even with biochemical B₁₂ deficiency; this complication can detected early by annual assessments of serum B₁₂ levels and prevented by annual intramuscular B₁₂ administration.
