Levomethorphan

Levomethorphan is the l-stereoisomer of methorphan. The effects of the two isomers are quite different. Dextromethorphan is an antitussive at low doses and a dissociative at much higher doses, whereas levomethorphan is an opioid analgesic. Levomethorphan has effects similar to levorphanol but is less potent as it must be demethylated to the active form by liver enzymes before becoming active. It can therefore be said to be the codeine analogue of levorphanol.

Levomethorphan is listed under the Single Convention On Narcotic Drugs 1961 and is regulated like morphine in most countries. In the United States it is a Schedule II Narcotic controlled substance with a DEA ACSCN of 9210 and 2013 annual aggregate manufacturing quota of 6 grammes. The salts in use are the tartrate (free base conversion ratio 0.64) and hydrobromide (0.77). At the current time, no levomethorphan pharmaceuticals are marketed in the United States.