A newly introduced drug may find many obstacles in its path. The intensity of marketing of new drugs can have unwanted effects. When new drugs are prescribed for a population that differs widely from that in clinical trials, unforeseen side effects can occur. The examples of troglitazone and mibefradil illustrate these mechanisms. It is the responsibility of the drug manufacturers and prescribers to let new drugs gradually find their therapeutic position. Otherwise exaggeration of untoward effects may lead to the speedy and possibly premature withdrawal of the drugs.