The so-called stimulant anorexiants, like phentermine, are believed to act via central catecholamine mechanisms. Side-effects include nervousness, insomnia, increased motor activity and cardiovascular disturbances such as tachycardia and elevation of blood pressure. The latter effects led physicians to feel that their use in obese hypertensive patients was very limited. Fenfluramine, although chemically related to the stimulant anorexiants, appears to act via serotonergic mechanisms. It reportedly causes sedation, occasionally diarrhea and few cardiovascular effects.