Morphinans

The pentacyclic opium skeleton: the poppy alkaloids and the semi-synthetics made from them — morphine, codeine, heroin, and the oxy- and hydro- derivatives. The skeleton alone does not make a compound an opioid agonist. Papaverine and noscapine are poppy alkaloids without meaningful opioid receptor activity; butorphanol, nalbuphine and pentazocine are mixed agonist-antagonists that can precipitate withdrawal in someone already dependent on a full agonist; and DXM, a morphinan by structure, is filed under Dissociatives because that is the experience.

Several members do nothing until the body converts them. Codeine depends on CYP2D6 to become morphine, and that enzyme varies widely between people and is blocked by common medicines, so the same amount is not the same drug in two bodies. Heroin acts through 6-monoacetylmorphine and morphine. Respiratory depression is the class risk, and it is additive with everything under Depressants.