Levomethorphan Clinical data ATC code Legal status Legal status
Pharmacokinetic data Elimination half-life 3-6 hours Identifiers
(1 R,9 R,10 R)-4-methoxy-17-methyl-17-azatetracyclo[220.127.116.11¹,¹⁰.0²,⁷]heptadeca-2(7),3,5-triene CAS Number PubChem CID ChemSpider UNII ChEBI ChEMBL CompTox Dashboard ( EPA) ECHA InfoCard 100.004.320 Chemical and physical data Formula C 18 H 25 N O Molar mass 271.397 g/mol g·mol −1 3D model ( JSmol)
(what is this?) (verify) Levomethorphan ( INN, BAN) is an opioid analgesic of the morphinan family that has never been marketed. It is the  L- stereoisomer of racemethorphan (methorphan). The effects of the two  isomers of the racemethorphan are quite different, with dextromethorphan (DXM) being an antitussive at low doses and a dissociative hallucinogen at much higher doses. Levomethorphan is about five times stronger than morphine. 
Levomethorphan is a
prodrug to levorphanol, analogously to DXM acting as a prodrug to dextrorphan or codeine behaving as a prodrug to morphine. As such, levomethorphan has similar effects to levorphanol but is less potent as it must be demethylated to the active form by  liver enzymes before being able to produce its effects. As a prodrug of levorphanol, levomethorphan functions as a potent  agonist of all three of the opioid receptors, μ, κ (κ 1 and κ 3 but notably not κ 2), and δ, as an NMDA receptor antagonist, and as a serotonin-norepinephrine reuptake inhibitor. Via activation of the KOR, levomethorphan can produce  dysphoria and psychotomimetic effects such as dissociation and hallucinations.
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 2014 annual aggregate manufacturing quota of 195 grams, up from 6 grams the year before. The salts in use are the tartrate (free base conversion ratio 0.644) and hydrobromide (0.958). At the current time, no levomethorphan pharmaceuticals are marketed in the United States.