Fenfluramine lowers plasma norepinephrine in overweight subjects.

The effect of fenfluramine on sympathetic nervous system activity was determined in 12 normotensive, obese men. Supine plasma norepinephrine (NE) concentrations decreased (p less than 0.001) from pretherapy levels (298 +/- 39 pg/ml) after one (166 +/- 30 pg/ml) and four weeks (171 +/- 28 pg/ml) of fenfluramine (60 mg daily). Fenfluramine did not alter the sympathetic nervous system responses to orthostasis or exercise. Fenfluramine-induced decreases in heart rate (72 +/- 3 to 67 +/- 4 beats/min, p less than 0.01) and mean arterial blood pressure (90 +/- 2 to 81 +/- 2 mmHg; p less than 0.005) were observed after only one week of therapy despite no significant change in body weight. We conclude that fenfluramine may be a useful agent in the treatment of patients with sympathetic hyperactivity. The effects of fenfluramine on given subsets of patients and control subjects are also defined.