Note: This document contains side effect information about acetaminophen / diphenhydramine. Some of the dosage forms listed on this page may not apply to the brand name Headache Relief PM.
Applies to acetaminophen / diphenhydramine: oral capsule, oral tablet
WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:
All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:
These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.
You may report side effects to the FDA at 1-800-FDA-1088. You may also report side effects at http://www.fda.gov/medwatch.
Applies to acetaminophen/diphenhydramine: oral capsule, oral liquid, oral tablet
The most commonly reported adverse reactions which are also related to use are drowsiness or sleepiness.
Frequency not reported: Severe and sometimes fatal dose-dependent hepatitis in alcoholic patients; hepatotoxicity from chronic acetaminophen therapy at therapeutic doses has occurred despite a lack of risk factors for toxicity
Postmarketing reports: Hepatic dysfunction
Alcoholic patients may develop hepatotoxicity after even modest doses of acetaminophen. In healthy patients, approximately 15 grams of acetaminophen is necessary to deplete liver glutathione stores by 70% in a 70 kg person. However, hepatotoxicity has been reported following smaller doses. Glutathione concentrations may be repleted by the antidote N-acetylcysteine. One case report has suggested that hypothermia may also be beneficial in decreasing liver damage during overdose.
In a recent retrospective study of 306 patients admitted for acetaminophen overdose, 6.9% had severe liver injury but all recovered. None of the 306 patients died.
Rare (less than 0.1%): Hypersensitivity including anaphylaxis and fixed drug eruptions
Frequency not reported: Rash, pruritus, eczema, photosensitivity, urticaria, dyspnea, angioedema
The CNS depressant effect of diphenhydramine parallels its plasma concentrations. The plasma concentration threshold for sedation is 30 to 42 ng/mL, and to cause mental impairment is 58 to 74 ng/mL.
Dystonic reactions have been accompanied by dizziness, mental confusion, rigidity, lip and tongue protrusion, trismus, torticollis, and swallowing difficulties and generally resolve spontaneously. Toxic encephalopathy has been reported in a child with chicken pox treated generously with topical diphenhydramine.
Delirium has been reported in elderly patients with mild dementia following a small oral dose of diphenhydramine.
Frequency not reported: Dizziness, difficulty concentrating, unsteadiness
Very common (10% or more): Drowsiness, sedation, convulsions, headache, paraesthesia, dyskinesias, toxic encephalopathy, delirium
Frequency not reported: Irritability, nervousness, anxiety, hallucinations, paradoxical excitation
Frequency not reported: Hypotension
Frequency not reported: Hypotension, tachycardia, palpitations
Rare (less than 0.1%): Acute pancreatitis
Frequency not reported: Nausea, dry mouth, dyspepsia, constipation
Rare (less than 0.1%): Acute tubular necrosis, interstitial nephritis
Acute tubular necrosis usually occurs in conjunction with liver failure, but has been observed as an isolated finding in rare cases.
Rare (less than 0.1%): Thrombocytopenia, methemoglobinemia (with resulting cyanosis in the setting of acute overdose)
Rare (less than 0.1%): Hemolytic anemia, thrombocytopenia, agranulocytosis
Rare (less than 0.1%): Serious skin reactions including erythematous skin rashes, bullous erythema and purpura fulminans, Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and acute generalized exanthematous pustulosis (AGEP)
Frequency not reported: Blurred vision
Frequency not reported: Urinary retention, dysuria, urinary difficulty
Rare (less than 0.1%): Eosinophilic pneumonia
Postmarketing reports: Bronchospasm
Frequency not reported: Thickening of bronchial secretions
Frequency not reported: Twitching or jerking muscles
Medically reviewed by BestRx Medical Team Last updated on 1/1/2020.
Source: Drugs.com Headache Relief Pm