The molecular structure of morphine consists of four parts:

① Phenanthrene hydride nuclei with four double bonds (rings A, B and C).

② N- methylpiperidine ring and phenanthrene nucleus ring B are fused.

③ oxygen bridge connecting ring A and ring C..

(4) Phenolic hydroxyl group on ring A and alcohol hydroxyl group on ring C ... When the hydroxyl hydrogen atom of phenol is replaced by methyl, the analgesic effect is weakened (such as codeine), and when the tertiary amine nitrogen is replaced by allyl, the analgesic effect is weakened and it becomes an antagonist of morphine, such as allyl morphine and naloxone.