Lifestyle changes and the diabetes medication metformin are effective against weight gain associated with antipsychotic treatment, especially when they are combined, according to an article in the January 9 issue of the Journal of the American Medical Association.

Metformin is a drug used to treat type 2 diabetes. It inhibits glucose production, is well tolerated, and prevents continual weight gain while it decreases measures of insulin resistance. Some studies have found that metformin can reduce body weight in patients with type 2 diabetes and in obese people who do not have diabetes, according to background information in the article.

Ren-Rong Wu, MD, of the Mental Health Institute of the Second Xiangya Hospital, Central South University, China, and colleagues conducted a clinical trial from October 2004 to December 2006 to test the efficacy of lifestyle intervention and metformin alone and in combination for antipsychotic-induced weight gain and abnormalities in insulin sensitivity.

The study included a total of 128 adult patients with schizophrenia. Participants who gained more than ten percent of their pre-drug weight were randomized to one of four treatment groups: 12 weeks of placebo, 750 mg daily metformin, 750 mg daily metformin with lifestyle intervention, or lifestyle intervention alone. Lifestyle interventions included psycho-educational, dietary, and exercise programs.

"In this 12-week study, we found statistically significant decreases in mean weight, body mass index, waist circumference, insulin, and insulin resistance index among patients in the lifestyle-plus-metformin, metformin-alone, and lifestyle-plus-placebo groups, but not among those in the placebo-alone group whose measurements continued to increase," the authors wrote.

Those taking metformin in combination with lifestyle intervention had average decreases of 1.8 in body mass index, 3.6 in insulin resistance index, and two cm in waist circumference. Those taking metformin alone showed average decreases of 1.2 in body mass index, 3.5 in insulin resistance index, and 1.3 cm in waist circumference. In the lifestyle-plus-placebo group, participants had average decreases of 0.5 in body mass index and 1.0 in insulin resistance index. Participants in the placebo group continued to show increases in all measures: 1.2 in body mass index, 0.4 in insulin resistance index, and 2.2 cm in waist circumference.

"Lifestyle intervention and metformin alone and in combination demonstrated efficacy for antipsychotic-induced weight gain. Lifestyle intervention plus metformin showed the best effect on weight loss," the authors concluded. "Metformin alone was more effective in weight loss and improving insulin sensitivity than lifestyle intervention alone."