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Naloxone chemical structure


IUPAC name
CAS number
ATC code


Chemical formula C19H21NO4
Molecular weight 327.27
Bioavailability 2% (90% absorption but high first-pass metabolism)
Metabolism Liver
Elimination half-life 1-1.5 hours
Excretion Urine, Biliary
Pregnancy category B (USA)
B1 (Aus)
Legal status Schedule 4 (Aus)
Routes of administration IV, IM

Naloxone is a drug used to counter the effects of opioid overdose, for example heroin and morphine overdose. Specifically, naloxone is used in opioid overdoses for countering life-threatening depression of the central nervous system and respiratory system. It is marketed under trade names including Narcan, Nalone, and Narcanti and has sometimes been mistakenly called "naltrexate." It is also not to be confused with Naltrexone, another opioid antagonist that has qualitatively different effects.


Naloxone has an extremely high affinity for μ-opioid receptors in the central nervous system. Naloxone is a μ-opioid receptor competitive antagonist, and its rapid blockade of those receptors often produces rapid onset of withdrawal symptoms. Naloxone also has an antagonist action, though with a lower affinity, at κ- and δ-opioid receptors.


Naloxone is synthesized from thebaine. The chemical structure of naloxone resembles that of oxymorphone, the only difference being the substitution of the N-methyl group with an allyl (prop-2-enyl) group. The name naloxone has been derived from N-allyl and oxymorphone.


Naloxone is injected, usually initially intravenously for fastest action. The drug acts after about two minutes, and its effects may last about 45 minutes. Other routes, including intramuscular injection and intranasal injection (use of a wedge device attached to the syringe to create a mist delivering the drug to the nasal mucosa) may also be utilized, although these are more likely in the prehospital setting.


Naloxone has been distributed as part of emergency kits to heroin users, and this has been shown to reduce rates of fatal overdose. Projects of this type are underway in San Francisco, New Mexico, Philadelphia, New York State, Baltimore, Boston, Los Angeles and Chicago, with pilot projects started in Scotland in 2006.

The drug also blocks the action of pain-lowering endorphins which the body produces naturally. The likely reason for this is that these endorphins operate on the same opioid receptors. In one experiment, women treated with naloxone reported higher pain levels during childbirth than women not so treated; in another experiment, the pain lowering effect of placebos was blocked if the placebos were administered along with naloxone.

While naloxone is still often used in emergency treatments for opioid overdose, its clinical use in the long-term treatment of opioid addiction is being increasingly superseded by naltrexone. Naltrexone is structurally similar but has a slightly increased affinity for κ-opioid receptors over naloxone, can be administered orally and has a longer duration of action.

Enteral naloxone has been successfully used in the reduction of gastritis and oesophagitis associated with opioid therapy in mechanically-ventilated acute care patients.

The effect of the hallucinogenic plant Salvia Divinorum and its primary active chemical Salvinorin-A, a κ-opioid agonist, can be inhibited by the pre-administration of naloxone, as well as PCP, ketamine, and dextromethorphan.

Naloxone is also being used as a secondary chemical in the FDA approved medicine Suboxone. Suboxone and Subutex were created as part of a detox program to well help opiate addicted patients stop using opiates. Suboxone contains 4 parts Buprenorphine and 1 part Naloxone. While Subutex contains only Buprenorphrine.

The Naloxone was placed in the Suboxone in an effort to dissuade patients from grinding up the Suboxone tablet and using it as part of a combination of opiates that the user would inject into their body. The Naloxone will block the effects of any opiates and cause the user to go into immediate withdrawal.

The Naloxone has no other use in Suboxone other than preventing users from injecting the Suboxone in the body. However, the Naloxone in Suboxone does cause side effects in some people. These side effects include, but are not limited to, asthenia, chills, headache, infection, pain, pain in the abdomen, back pain, withdrawal syndrome, vasodilation, constipation, diarrhea, nausea, vomiting, insomnia, and sweating. Other than patients who might inject opiates, there is no reason for Naloxone in Suboxone. Because of these side effects, the FDA recommends that doctors begin any chemical detox using Subutex, which does not contain any Naloxone. By this manner, if for some reason the doctor moves the patient to Suboxone and the patient begins having side effects related to Naloxone, the doctor can easily move the patient back to Subutex.

For these reasons and others, it has been reported that Subutex is easier to withdraw from than is Suboxone.

Legal status

The patent for Naloxone has expired and it is manufactured by various companies.


The CAS number of naloxone is 465-65-6; the anhydrous hydrochloride salt has CAS 357-08-4 and the hydrochloride salt with 2 molecules of water has CAS 51481-60-8.

External links

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