Except for codeine, pethidine is the most widely used of all narcotics. It was synthesized in 1939 in a search for new spasmolytic drugs of the atropine type. Its analgesic properties then came to light; but the notion that the drug is spasmolytic, anti-colic, or relaxant to smooth muscle, has been persistent. It was also believed at first to be more analgesic, less addicting, and less prone to cause nausea, vomiting and respiratory depression than morphine. All of these impressions were formed at a time when it was often assumed that pharmacological effects in animals would necessarily occur in man; and when the principles of the controlled clinical trial were not widely understood.