Clinical data
Routes of
ATC code N02AD02 (WHO)
Legal status
Legal status
Synonyms Fenazocina, Phenazocinum, DEA No. 9715
CAS Number 127-35-5 N
PubChem (CID) 14707
ChemSpider 391631 N
ECHA InfoCard 100.004.397
Chemical and physical data
Formula C22H27NO
Molar mass 321.45588 g/mol
3D model (Jmol) Interactive image
 NYesY (what is this?)  (verify)

Phenazocine (brand names Prinadol, Narphen) is an opioid analgesic drug, which is related to pentazocine and has a similar profile of effects.

Effects of phenazocine include analgesia and euphoria, also may include dysphoria and hallucinations at high doses, most likely due to action at κ-opioid and σ receptors.[1]

Phenazocine appears to be a much stronger analgesic with fewer side effects than pentazocine, probably due to a more favorable μ/κ binding ratio. Phenazocine is a much more potent analgesic than pentazocine and other drugs in the benzomorphan series, most probably due to the presence of an N-phenethyl substitution, which is known to boost μ-opioid activity in many classes of opioid analgesics.[2]

Consequently, phenazocine is some 4x the potency of morphine as an analgesic. Also it does not cause spasm of the sphincter of Oddi, making it more suitable than morphine for the treatment of biliary or pancreatic pain.[3]


Phenazocine was invented in the 1950s.[4][5] It was one of a number of benzomorphan opioids (including pentazocine, dezocine, and cyclazocine) developed in the search for non-addictive strong analgesics.

Phenazocine was once widely used, and was mainly supplied as 5 mg tablets of the hydrobromide salt for sublingual use (Narphen, Prinadol and other names), but its use was discontinued in the United Kingdom in 2001.[6]

Phenazocine was briefly used in the United States but fell out of favour for the above-mentioned reasons; it remains a Schedule II substance under the Comprehensive Drug Abuse Control & Prevention Act (aka Controlled Substances Act) of 1970 (CSA) but is not manufactured; other Schedule II narcotics not in use in the United States include bezitramide and metopon. The DEA ACSCN for phenazocine is 9715 and its 2013 annual manufacturing quota was 6 grammes [7]


  1. Harris LS, Pierson AK (February 1964). "Some Narcotic Antagonists in the Benzomorphan Series". Journal of Pharmacology and Experimental Therapeutics. 143: 141–8. PMID 14163985.
  2. Feinberg AP, Creese I, Snyder SH (November 1976). "The opiate receptor: a model explaining structure-activity relationships of opiate agonists and antagonists". Proceedings of the National Academy of Sciences USA. 73 (11): 4215–9. doi:10.1073/pnas.73.11.4215. PMC 431391Freely accessible. PMID 186791.
  3. Hopton D. (January 1971). "Double-blind clinical trial of the analgesic effects of phenazocine hydrobromide (Narphen) compared with morphine sulphate in patients with acute abdominal pain". Gut. 12 (1): 51–4. doi:10.1136/gut.12.1.51. PMC 1411461Freely accessible. PMID 4929685.
  4. Clarke EG (August 8, 1959). "Identification of Phenazocine, a Potent New Analgesic". Nature. 184 (Suppl 7): 451–451. doi:10.1038/184451a0. PMID 13810504.
  5. Eckenhoff JE (May–June 1959). "Phenazocine, a new benzomorphan narcotic analgesic". Anesthesiology. 20 (3): 355–8. doi:10.1097/00000542-195905000-00016. PMID 13650222.
  6. "Monthly Release Terming and Coding Newsletter" (PDF). NHS Information Authority. February 2001. Retrieved 2008-01-11.
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