Genapap PM Side Effects
Generic name: acetaminophen / diphenhydramine
Medically reviewed by Drugs.com. Last updated on Jul 31, 2022.
Note: This document contains side effect information about acetaminophen / diphenhydramine. Some dosage forms listed on this page may not apply to the brand name Genapap PM.
Applies to acetaminophen / diphenhydramine: oral tablet.
Serious side effects of Genapap PM
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:
- Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
- Signs of liver problems like dark urine, feeling tired, not hungry, upset stomach or stomach pain, light-colored stools, throwing up, or yellow skin or eyes.
- Not able to pass urine or change in how much urine is passed.
- A very bad skin reaction (Stevens-Johnson syndrome/toxic epidermal necrolysis) may happen. It can cause very bad health problems that may not go away, and sometimes death. Get medical help right away if you have signs like red, swollen, blistered, or peeling skin (with or without fever); red or irritated eyes; or sores in your mouth, throat, nose, or eyes.
Other side effects of Genapap PM
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:
- Feeling sleepy.
- Feeling nervous and excitable.
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 1-800-332-1088. You may also report side effects at https://www.fda.gov/medwatch.
For Healthcare Professionals
The most commonly reported adverse reactions which are also related to use are drowsiness or sleepiness.[Ref]
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[Ref]
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.
Rare (less than 0.1%): Hypersensitivity including anaphylaxis and fixed drug eruptions
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.
Frequency not reported: Dizziness, difficulty concentrating, unsteadiness
Frequency not reported: Hypotension
Rare (less than 0.1%): Acute pancreatitis
Acute tubular necrosis usually occurs in conjunction with liver failure, but has been observed as an isolated finding in rare cases.[Ref]
Rare (less than 0.1%): Acute tubular necrosis, interstitial nephritis[Ref]
Rare (less than 0.1%): Thrombocytopenia, methemoglobinemia (with resulting cyanosis in the setting of acute overdose)
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)[Ref]
Frequency not reported: Blurred vision[Ref]
Rare (less than 0.1%): Eosinophilic pneumonia
Postmarketing reports: Bronchospasm
Frequency not reported: Thickening of bronchial secretions[Ref]
Frequency not reported: Twitching or jerking muscles[Ref]
More about Genapap PM (acetaminophen / diphenhydramine)
Related treatment guides
1. "Product Information. Tylenol Extra Strength PM (acetaminophen-diphenhydramine)." Johnson and Johnson/Merck (2005):
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Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
Some side effects may not be reported. You may report them to the FDA.