Narcan Side Effects

Generic Name: naloxone

Note: This document contains side effect information about naloxone. Some of the dosage forms listed on this page may not apply to the brand name Narcan.

Some side effects of Narcan may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

For the Consumer

Applies to naloxone: parenteral injection

Side effects include:

Nausea and vomiting rarely postoperatively with parenteral dose exceeding that usually recommended; a causal relationship has not been established.

Analgesia reversal, excitement, agitation, and increased BP may occur with excessive postoperative doses.

Postoperative use: Hypotension, hypertension, ventricular tachycardia and fibrillation, dyspnea, pulmonary edema, and cardiac arrest; sequelae include death, coma, and encephalopathy.

Opiate overdosage: Tremor and hyperventilation associated with an abrupt return to consciousness.

Opiate dependence: Abrupt dependence reversal may precipitate acute withdrawal.

Adverse cardiovascular effects have occurred most frequently in postoperative patients with preexisting cardiovascular disease or in those receiving other drugs that produce similar adverse cardiovascular effects. (See Cardiovascular Disease under Cautions.)

For Healthcare Professionals

Applies to naloxone: compounding powder, injectable solution


Naloxone may precipitate withdrawal in patients receiving opioids. Withdrawal is characterized by nausea, vomiting, sweating, lacrimation, rhinorrhea, cramping, insomnia, chills/hot flashes, piloerection, tachycardia, anxiety, restlessness, irritability, tremulousness, hypertension, seizures, and cardiac arrest. Ophthalmic naloxone (the active ingredient contained in Narcan) administration may elicit withdrawal. Similar symptoms have been noted in patients with pruritus of cholestasis who were not receiving opioids.

Withdrawal syndromes may be precipitated by as little as 0.05 to 0.2 mg intravenously in patients taking 24 mg per day of methadone.


Cardiovascular side effects have included hypotension, hypertension, atrial and ventricular tachycardia, ventricular fibrillation, left ventricular failure, and cardiac arrest. These effects occurred in postoperative patients, many of whom had cardiovascular disease.

A 45-year-old male narcotic addict and alcoholic with hepatitis and undiscovered cardiomyopathy was given 0.8 mg of naloxone intravenously over a 2 minute period and developed ventricular fibrillation. The patient required naloxone once more for this episode and again developed ventricular fibrillation. A second opiate overdose in the same patient was treated with an initial dose of 0.4 mg intravenously, followed by 0.4 mg intravenously, then intramuscularly. Each time the patient developed ventricular fibrillation responsive to cardioversion and/or lidocaine.

Severe hypertension (mean arterial pressure rising from a baseline of 107 mmHg to 147 mmHg in about 2 to 3 hours) has been reported in an essential hypertension patient given an initial 8 mg dose intravenously, followed by an infusion of 0.13 mg/min over the next 2.5 hours. When the naloxone was discontinued the blood pressure quickly returned to normal.

Mild hypotension and one case of moderate hypertension were observed in patients receiving a bolus of 4 mg/kg followed by 2 mg/kg/hour for 24 hours. One study reported that the newborn infants of mothers who have received naloxone near term may experience tachycardia.


Respiratory side effects have rarely included with pulmonary edema.

Pulmonary edema has occurred within 60 seconds of administration and at dosages as low as 0.1 mg in adults. Patients ranged from healthy (postoperative) to ill with conditions such as congestive heart failure and cardiopulmonary failure.

Three cases, treated with numerous drugs, developed clinical evidence of pulmonary edema shortly after intravenous administration of naloxone (0.3 to 1.6 mg).

Nervous system

A 51-year-old male was given 0.8 mg of naloxone (the active ingredient contained in Narcan) for obtundation. Within 30 seconds of administration a grand mal seizure occurred. The patient had Pseudomonas sepsis with negative CSF cultures.

Seizures and paresthesias have been reported at both standard and high dosages.

Seizures have been reported in 5% of patients receiving a bolus of 4 mg/kg followed by 2 mg/kg/hr for 24 hours.

Nervous system side effects have included seizures, paresthesias, agitation (3%), tremors (3%), and headache (5%). Agitation, tremors, headache, alteration in mood and cognition, mental discomfort, sleepiness, and confusion have been reported rarely at high dosages. Lethargy has been reported in manic and control patients. Naloxone administration may worsen obsessive compulsive behavior.


Gastrointestinal side effects reported in patients receiving high dose therapy have included nausea and vomiting.

Nausea and/or vomiting occurred in 32% of patients in one study who received a bolus of 4 mg/kg followed by 2 mg/kg/hr for 24 hours.


Genitourinary side effects have rarely included urinary urgency. Naloxone (the active ingredient contained in Narcan) may have a mild diuretic effect.

A 75-year-old was treated with naloxone for senile dementia. A dosage of 0.8 mg in 25 mL of normal saline was given as an infusion over 10 minutes. The treatment was given 6 times, each time the patient experienced urinary urgency (at least 5 small volume urinations over 2 hours).

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