Phenazocine

Phenazocine (brand names Prinadol, Narphen) is an opioid analgesic drug, which is related to pentazocine and has a similar profile of effects.

Effects of phenazocine include analgesia and euphoria, also may include dysphoria and hallucinations at high doses, most likely due to action at κ-opioid and σ receptors. Phenazocine appears to be a much stronger analgesic with fewer side effects than pentazocine, probably due to a more favorable μ/κ binding ratio. Phenazocine is a much more potent analgesic than pentazocine and other drugs in the benzomorphan series, most probably due to the presence of an N-phenethyl substitution, which is known to boost μ-opioid activity in many classes of opioid analgesics. Also, it does not cause spasm of the sphincter of Oddi, making it more suitable than morphine for the treatment of biliary or pancreatic pain.

Regarding the two enantiomers of phenazocine, (R)-phenazocine has twenty times the potency of morphine as an analgesic, while (S)-phenazocine has about four times the potency of morphine.