While it is true that dextromethorphan is not technically a member of the opiate family, it is distantly related in its chemical composition. Dextromethorphan is created by from levomethorphan, which is classified as an opioid, the synthetic or semi-synthetic relatives of the natural chemical family called the opiates. Levomethorphan has most of the same qualities of all drugs in the opiate and opioid classes. This includes strong suppressive effects on the respiratory system. It is these strong effects on the respiratory system that make dextromethorphan an effective anti-cough agent. Opiate and opioid compounds have anti-cough properties but produce greater overall respiratory depression than dextromethorphan.

It was initially believed that dextromethorphan preserved the anti-cough properties of the opioid drugs but not many of the other therapeutic and harmful effects of the opioid class. This is why dextromethorphan was not included in the list of drugs comprising the...