Introduction of a phenyl group to the 4-position of the piperidine-ring produces a drug 60-fold more potent than morphine.

[4] The most potent reported derivative is 4-hydroxy-4-phenyl phenapromide which displays analgesic activity some x150 greater than morphine.

[5] Phenampromide produces similar effects to fentanyl, including analgesia, sedation, dizziness and nausea.

Phenampromide is in Schedule I of the Controlled Substances Act 1970 of the United States as a narcotic with ACSCN 9638 with a zero aggregate manufacturing quota as of 2014.

The free base conversion ratio for salts includes 0.88 for the hydrochloride.