Narcan prevents or reverses the effects of opioids including respiratory depression, sedation, and hypotension. Narcan does not produce respiratory depression, psychotomimetic effects, or pupillary constriction. In the absence of narcotics or agonistic effects of other narcotic antagonists it exhibits essentially no parhacologic activity.

In the presence of physical dependence on narcotics, Narcan will produce withdrawal symptoms.

Mechanisms of Action

While the mechanism of action of Narcan is not fully understood, the preponderance of evidence suggests that Narcan antagonizes the opioid effects by competing for the same receptor sites.

When Narcan is administered intravenously, the onset of action is generally apparent within two minutes; the onset of action is only slightly less rapid when it is administered subcutaneously or intramuscularly. The duration of action is dependent upon the dose and route of administration of Narcan. Intramuscular administration produces a more prolonged effect than intravenous administration. The requirement for repeat doses of Narcan, however, will also be dependent upon the amount, type, and route of administration of the narcotic being antagonized.

Following parenteral administration, Narcan is rapidly distributed throughout the body,. It is metabolized by the liver, primarily by blucoronide conjugation and excreted in urine. In one study the serum half-life in adults ranged from 30 to 81 minutes.

Indications and usage

Narcan is indicated for the complete or partial reversal of narcotic depression, including respiratory depression, induced by opioids including natural and synthetic narcotics, propoxyphene, metadone, and certain narcotic-antagonist analgesics: nalbuphine, pentazocine, and butorphanol.


Narcan is contraindicated in patients known to be hypersensitive to it.

-- Taken from the Physician's Desk Reference, 1993 edition. Remainder of entry omitted.