Acetaminophen
- Also Known As:
- Paracetamol

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.At a Glance
Why Get Tested?
To determine if an overdose has occurred and if an antidote is required; to determine risk of liver damage and to help monitor the outcome of antidote treatment
When To Get Tested?
When it is suspected that a person has ingested an overdose of acetaminophen or has signs and symptoms of toxicity, such as nausea, vomiting, and abdominal pain; when following a patient, every 4 to 6 hours after an overdose of the drug is ingested
Sample Required?
A blood sample drawn from a vein
Test Preparation Needed?
None
What is being tested?
Acetaminophen is one of the most common pain relievers (analgesics) and fever reducers (antipyretics) available over the counter. It is generally regarded as safe. However, it is also the most common cause of toxic hepatitis in North America and Europe and one of the most common poisonings from either accidental or intentional overdose.
Once entering your body, like many other medications, acetaminophen is processed in the liver into harmless substances and removed in your urine. However, about 5 to 10% of the absorbed acetaminophen is converted to a toxic, highly-reactive byproduct. Fortunately, your liver makes a antioxidant called glutathione that binds to the byproduct and minimizes its toxic effects. When a large dose of acetaminophen is ingested or that exceeds the recommended amount over a period of time, the liver is no longer able to produce enough protective glutathione; as a result, the toxic byproduct builds up in the liver and may cause severe liver damage if timely treatment is not given.
For this reason, acetaminophen can be harmful or even fatal if not taken correctly and children in particular are at risk if caregivers do not follow dosing instructions carefully. Often, people do not realize that acetaminophen is one of the ingredients in many combination medications such as cold and flu preparations. If two or more of these medications are taken together, levels of acetaminophen may exceed safe limits.
Acetaminophen preparations come in varying strengths and several different forms, including tablets, capsules and liquid.
- For adults, the typical maximum daily limit for acetaminophen is 4000 milligrams (mg). Consuming more than 4000 mg in a 24-hour period is considered an overdose, while ingesting more than 7000 mg can lead to a severe overdose reaction unless treated promptly.
- For children, the amount that is considered an overdose depends on their age and body weight. (For more on this, see the MayoClinic webpage Acetaminophen and children: Why dose matters.)
If it is known or suspected that someone has ingested an overdose of acetaminophen, it is recommended to take the person to the emergency room. If a health practitioner determines that an overdose has occurred, treatment may include an antidote, N-acetylcysteine (NAC), which can help minimize damage to the liver, especially if given within 8 to 12 hours after an overdose. Though NAC is ideally administered within this timeframe, people who seek treatment more than 12 hours after ingestion may still be given the antidote.
Until recently, NAC for people who visit health care providers later than 24 hours after acetaminophen ingestion was not the standard of care for acetaminophen overdose management in the United States. However, study data from England suggest that NAC may be beneficial for acetaminophen-induced liver failure more than 24 hours after ingestion.
Common Questions
View Sources
Sources Used in Current Review
2019 Review performed by Li-Sheng Chen, PhD, DABCC, FACB.
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(Last updated 3/29/2017) MayoClinic. Acetaminophen and children: Why dosage matters. Available online at https://www.mayoclinic.org/healthy-lifestyle/childrens-health/in-depth/acetaminophen/art-20046721. Accessed January 2019.
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