Amantadine (Symmetrel, Endantadine), a drug used to treat Parkinson’s disease as well as the flu, may help stabilize weight in patients taking the antipsychotic drug olanzapine (Zyprexa), researchers report in the American Journal of Psychiatry.

Dr. Karen A. Graham and colleagues from the University of North Carolina, Chapel Hill, note that weight gain “is the most important tolerability issue” for antipsychotics, such as olanzapine.

To investigate whether amantadine might combat such weight increase, the researchers randomly selected 21 psychiatric patients who had gained at least 5 lbs. with olanzapine to also receive amantadine or inactive “placebo”.

The researchers assessed body mass index (BMI), a measure of body weight relative to height, as well as psychiatric status and fasting blood sugar levels when the study began and at 12 weeks.

Prior to the study, each patient had been treated with olanzapine for around 7 months. When the study began, the average BMI in each group was about 32, indicating that the subjects were generally overweight. Three patients in the amantadine group and none in the placebo group withdrew from the study.

Significantly fewer patients in the amantadine group gained weight compared to the placebo group. The amantadine patients lost 0.8 lbs., on average, and had a drop in BMI of 0.07, the placebo patients gained 8.7 lbs. and had a BMI increase of 1.24.

Overall, weight stabilization or loss was seen in 67 percent of the amantadine-treated patients compared with just 22 percent of those given placebo.

The researchers note that the mechanism by which amantadine stabilizes weight is unknown, but that prevention of antipsychotic-related Obesity is critical.

“Investigation of the use of amantadine started concurrently with antipsychotic medication is imperative,” they conclude.

SOURCE: American Journal of Psychiatry, September 2005.