Myrophine is an opiate analog and long-acting prodrug for morphine with a slow onset of effects. It is weaker than morphine as an analgesic but longer-lasting in effects and was thought to have a more local anesthetic effect than morphine, though with a somewhat greater tendency to cause histamine reactions like itching and rash. In addiction studies conducted in human subjects in the 1950s, myrophine did not substitute for morphine in withdrawal, did not produce notable morphine-like effects, and did not produce addiction or dependence regardless of dose or how it was administered.

Myrophine:
https://drugs.ncats.io/substance/417TUP54OL

an opiate analogue that was developed in 1952. It is a derivative of morphine. it was thought to be useful in treating pain in addicts who were being detoxified from other opioid drugs.