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Systematic (IUPAC) name
6,14-endoetheno – 7 a (1-(R)-hydroxy-1 methylbutyl)-tetrahydro-nororipavine
CAS number 14521-96-1
ATC code  ?
PubChem  ?
Chemical data
Formula C25H33NO4 
Mol. mass 411.53 g/mol
Pharmacokinetic data
Bioavailability  ?
Metabolism  ?
Half life  ?
Excretion  ?
Therapeutic considerations
Pregnancy cat.


Legal status

List 1NL Schedule I/II(see text)US

Routes  ?

Etorphine (Immobilon® or M99) is a semi-synthetic opioid possessing an analgesic potency approximately 40,000 times that of morphine. It was invented in 1963 by a research group at McFarlan-Smith and Co. in Edinburgh, led by Professor Kenneth Bentley.[1][2] It can be produced from thebaine. It is most often used to immobilize elephants and other large mammals. Etorphine is only available legally for veterinary use and is strictly governed by law. Diprenorphine (M5050) is an opioid receptor antagonist that can be administered in proportion to the amount of etorphine used (1.3 times) to reverse its effects. Veterinary-strength etorphine is fatal to humans; one drop on the skin can cause death within a few minutes.[3]

Large Animal Immobilon is a combination of etorphine plus acepromazine maleate. An etorphine antidote Large Animal Revivon contains mainly diprenorphine for animals and a human-specific naloxone-based antidote, which should be prepared prior to the etorphine.

A close relative, dihydroetorphine has been used as opiate painkiller for human usage in China. It is claimed to be less addictive than traditional opioids but this has yet to be confirmed.



Etorphine is an agonist at μ, δ, and κ opioid receptors. It also has a weak affinity for the ORL1 nociceptin/orphanin FQ receptor.[4]

Legal status

In Hong Kong, Etorphine is regulated under Schedule 1 of Hong Kong's Chapter 134 Dangerous Drugs Ordinance. It can only be used legally by health professionals and for university research purporses. The substance can be given by pharmacists under a prescription. Anyone who supplies the substance without prescription can be fined $10000(HKD). The penalty for trafficking or manufacturing the substance is a $5,000,000 (HKD) fine and life imprisonment. Possession of the substance for consumption without license from the Department of Health is illegal with a $1,000,000 (HKD) fine and/or 7 years of jail time.

In the Netherlands, Etorphine is a list I drug of the Opium Law. It is only used for veterinary purposes in zoo's to inmobilise large animals.

In the US, Etorphine is listed as a Schedule I drug, although Etorphine hydrochloride is classified as Schedule II.

In popular culture

Etorphine is the drug which the main character in the books and TV-series about the serial killer and blood spatter specialist Dexter uses to immobilize his victims. In one episode of the TV-series it is shown that the character uses a fake doctor's name to obtain the controlled substance.


  1. ^ Bentley KW, Hardy DG. "New potent analgesics in the morphine series." Proceedings of the Chemical Society. 1963;220.
  2. ^ Bentley KW, Hardy DG. "Novel analgesics and molecular rearrangements in the morphine-thebaine group. 3. Alcohols of the 6,14-endo-ethenotetrahydrooripavine series and derived analogs of N-allylnormorphine and -norcodeine." Journal of the American Chemical Society. 1967 Jun 21;89(13):3281-92. PMID 6042764
  3. ^ Zoo Vet At Large - Sky Travel (8 July 2007, Part 10 of 26)
  4. ^ Hawkinson JE, Acosta-Burruel M, Espitia SA. "Opioid activity profiles indicate similarities between the nociceptin/orphanin FQ and opioid receptors." European Journal of Pharmacology. 2000 Feb 18;389(2-3):107-14. PMID 10688973
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Etorphine". A list of authors is available in Wikipedia.
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