Reserchers in US recently confirmed that fenfluramine use as appetite suppressant can cause heart valve problems. Though this problem is mild it could be life threatening. The heart problem improves or disapers after the drug is discontinued.

This drug is known to cause palpitation, depression, pulmonary hypertension, vomiting, sleep disturbances, even congestive heart failure.

Fenfluramine acts on the central nervous system to inhibit the feeding centre.  The diet drugs should not be taken to control appetite and a shotcut to slimming. Most of the weight loss drugs cause impressive weight loss in the beginning only. These drugs cause the body to go into starvation mode, when it responds by burning fewer calories and boosting appetite.
The starvation response is triggered because the weight loss causes a decline in blood levels of a hormone leptin. Reserchers are now trying a way out to keep the leptine level high by giving leptine along with the appetite suppressants like sibutramine. Small doses of leptin along with sibutramine tricks the brain into thinking enough leptin was in the body to allow the weight loss to continue.

Because of the seriousness of the valvular heart disease associated with the use of fenfluramine, the medication was withdrawn from the market in September of 1997.