Fenfluramine hydrochloride is a drug that suppresses appetite by altering brain levels of serotonin, formerly used in the management of obesity but withdrawn from the market in 1997 because of its potentially dangerous side effects. Cardiovascular - Palpitation, chest pain, tachycardia, arrhythmias and hypertension are common; cardiovascular collapse can occur in severe poisoning. Myocardial ischaemia, infarction and ventricular dysfunction are described. The oral administration of fenfluramine hydrochloride, which acts centrally to augment serotonin-mediated synaptic function, did not alter extra pyramidal signs in either untreated or levodopatreated parkinsonian patients. These results support the contention that biochemical indices of serotonergic dysfunction in Parkinson disease do not reflect a critical role for serotonin-containing neural systems in the path physiology of Parkinsonism and that serotonin-active drugs afford no significant therapeutic benefit to patients with this disorder. Serotonin level in platelet-poor plasma was assessed on all 12 visits. Serotonin levels decreased with the administration of fenfluramine, and increased with the reinstatement of placebo. Statistical tests revealed no significant differences on the IQ scores, the RLRS, or the ABS-SE for the drug versus the placebo conditions.