Codeine is a prodrug with basically no analgesic effects by itself. It instead must be metabolized (mostly by the liver via CYP2D6) into morphine in order to provide analgesia. Some folks convert more, some less.
abhishek021196Just a side note, CYP2D6 is responsible for metabolism of cardiovascular drugs. The dirty mnemonic is that since a 2D Echo is used to image the heart, CYP2D6 metabolizes CV drugs. +2020-03-23T07:12:43Z