but unpredictable proportion of users. Both of these targets were discovered as a result of high levels of distinctive side-effects during the marketing of certain medicines, and, while some older drugs with significant hERG activity are still used with caution, most drugs that have been found to be strong 5-HT_2B agonists were withdrawn from the market, and any new compound will almost always be discontinued from further development if initial screening shows high affinity for these targets.