Levomethorphan is the l-stereoisomer of methorphan

Methorphan

Methorphan comes in two isomeric forms, each with differing pharmacology and effects:* Dextromethorphan - An over-the-counter cough suppressant, as well as dissociative hallucinogen....

. The effects of the two isomers are quite different. Dextromethorphan

Dextromethorphan

Dextromethorphan is an antitussive drug. It is one of the active ingredients in many over-the-counter cold and cough medicines, such as Robitussin, NyQuil, Dimetapp, Vicks, Coricidin, Delsym, and others, including generic labels. Dextromethorphan has also found other uses in medicine, ranging...

 is an antitussive at low doses and a dissociative at much higher doses, whereas levomethorphan is an opioid

Opioid

An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract...

 analgesic

Analgesic

An analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....

. Levomethorphan has effects similar to levorphanol

Levorphanol

Levorphanol is an opioid medication used to treat severe pain. It is the levorotatory stereoisomer of the synthetic morphinan and a pure opioid agonist, first described in Germany in 1948 as an orally active morphine-like analgesic...

but is less potent as it must be demethylated to the active form by liver enzymes before becoming active.