Wiktionary
n. (context chemistry English) The inactive isomer of the opioid analgesic dextromoramide.
Wikipedia
Levomoramide is the inactive isomer of the opioid analgesic dextromoramide, invented by the chemist Paul Janssen in 1956. Unlike dextromoramide, which is a potent analgesic with high abuse potential, levomoramide is virtually without activity.
"Resolution reveals that the analgetic activity in this case resides almost entirely in the isomer."
"In the α-CH series, one of the optical isomers of each enantiomorphic pair is about twice as active as the racemic mixture; the other isomer is devoid of significant analgesic activity."
However, despite being inactive, levomoramide is scheduled by UN Single Convention on Narcotic Drugs.