Acetaminophen: 7 things you should know
Medically reviewed by Carmen Fookes, BPharm. Last updated on Jan 27, 2020.
1. How it works
- Acetaminophen is used to relieve pain. Experts aren't sure exactly how acetaminophen works, but suspect it blocks a specific type of cyclo-oxygenase (COX) enzyme, located mainly in the brain.
- Acetaminophen belongs to the class of medicines called analgesics (pain relievers); it is specifically a non-narcotic analgesic. It may also be called an antipyretic because it will bring down a fever.
- Effective for the temporary relief of minor aches, pains, and headache. May be used in the treatment of many conditions such as arthritis, backache, colds, menstruation pain, and toothache.
- Also, lowers a fever but does not control inflammation.
- First choice for mild-to-moderate pain due to its efficacy, minimal toxicity, and low cost.
- At low dosages, it lacks the gastrointestinal side effects associated with NSAID pain relievers (does not cause ulcerations, bleeding or perforations).
- May be combined with strong opioids for the treatment of severe pain.
- Available in a range of formulations including liquid, oral tablets, oral disintegrating tablets, chewable tablets, controlled-release tablets, dispersible tablets, injectable, and rectal preparations.
- Generic acetaminophen is available.
If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:
- Rarely, may cause itchiness, constipation, nausea, vomiting, headache, insomnia, and agitation. May cause gastrointestinal side effects at high dosages.
- The potential for liver damage exists, even at recommended dosages. The risk is increased with higher dosages, a shorter interval between doses, in people who drink three or more alcoholic drinks per day, when taken with other medications that also contain acetaminophen, and in patients with pre-existing liver disease.
- Considered less effective for pain relief than NSAIDs but associated with a lower risk of side effects.
- May not be suitable for some people including people who regularly consume three or more glasses of alcohol per day and those with liver disease.
- May interact with some other medications including warfarin.
Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects
- May be administered without regards to food; although food may decrease any reported stomach upset.
- Do not exceed the recommended dosage, because this may put you at risk of liver toxicity. Adults and teenagers who weigh at least 110 pounds (50kg) should not take more than 1000mg of acetaminophen in one dose or more than 4000mg in 24 hours. Children younger than 12 years should only take the dosage recommended to them on the label (this varies depending on their weight and age).
- Always seek your doctor's advice before administering acetaminophen to children aged less than two. If you are giving pediatric acetaminophen, always use the dosing syringe provided, or another suitable properly calibrated measure. Do NOT use a kitchen teaspoon.
- Shake liquid acetaminophen before use. Chewable tablets should be properly chewed before swallowing. Hands should be dry before handling the acetaminophen disintegrating tablet, then the tablet should be placed on the tongue and allowed to fully dissolve before swallowing. The acetaminophen disintegrating granules should be dissolved in at least four ounces of water; the mixture stirred, then drunk straight away.
- Be careful not to administer other products containing acetaminophen or paracetamol at the same time. Acetaminophen is often an ingredient in combination cold and flu remedies.
- Men should not drink more than two alcoholic drinks a day and women no more than one alcoholic drink per day while taking acetaminophen.
- Contact your doctor if symptoms worsen, you develop a skin rash, if redness or swelling occurs in the painful area, if your fever lasts longer than 3 days, or for persistent pain (excluding sore throat) of longer than 10 days in adults, 5 days in children and adolescents, or 3 days for infants.
- Contact your doctor immediately if you or your child have a sore throat that is severe, persists for longer than 2 days, or is followed by fever, rash, headache, nausea, or vomiting.
- Seek urgent medical attention if you develop pain in your upper abdomen, dark urine, loss of appetite, yellowing of the skin or eyes or clay-colored stools.
- Do not take acetaminophen without your doctor's advice if you are pregnant.
6. Response and Effectiveness
- The pain-relieving effects of acetaminophen occur within 30-60 minutes of administration of the oral tablets. The effects last for three to four hours.
Medicines that interact with acetaminophen may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with acetaminophen. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.
Common medications that may have a moderate interaction with acetaminophen include:
- anticonvulsants, such as fosphenytoin or phenytoin
Alcohol may enhance the liver toxicity of acetaminophen.
Note that this list is not all-inclusive and includes only common medications that may interact with acetaminophen. You should refer to the prescribing information for acetaminophen for a complete list of interactions.
Acetaminophen. Revised 07/2019. Drugs.com https://www.drugs.com/ppa/acetaminophen.html
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use acetaminophen only for the indication prescribed.
Copyright 1996-2020 Drugs.com. Revision date: January 26, 2020.
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
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