Open label study of the effect of amantadine on weight gain induced by olanzapine

The purpose of the present paper was to investigate the effects of the dopamine agonist amantadine in those patients with weight gain induced by olanzapine. An open trial was conducted in those patients who gained >3 kg in weight induced by olanzapine use. All subjects were evaluated by weight, body mass index (BMI), the Brief Psychiatric Rating Scale (BPRS), and the Extrapyramidal Symptom Rating Scale (ESRS) before and after the use of amantadine in addition to olanzapine. Twenty-five of 30 enrolled patients completed the present study. Mean bodyweight and BMI was increased by 6.44 +/- 4.42 kg and 5.04 +/- 3.47 kg/m2 significantly with olanzapine alone (P < 0.001). When amantadine and olanzapine were used together, the average weight and BMI decreased by 1.07 +/- 3.19 kg and 0.84 +/- 2.5 kg/m2, but did not have statistical significance. The average values of BPRS showed a significant decrease (P < 0.001). No significant changes were present in ESRS. Amantadine did not have an effect on weight gain induced by olanzapine. Randomized placebo-controlled prospective studies are needed.