This image shows the crystal structure of serotonin receptor (5HT2B) in complex with ergotamine. The background shows chemical structures of fenfluramine and phentermine (fen-phen), a popular anti-obesity treatment later withdrawn due to valvular heart disease and pulmonary hypertension. Fenfluramine activation of 5HT2B receptors was shown to be the culprit of these serious cardiovascular problems. A heart structure crossed by "Rx" highlights the troubled history of fen-phen. Since then, many drugs have been shown to have the same side-effect in humans including drugs used in treating migraine headaches (ergotamine, dihydroergotamine), Parkinson's Disease (cabergoline, pergolide) and other disorders (Benfluorex). (Image courtesy of the Stevens lab.)