Acetaminophen: common pain relief with a narrow margin for overdose

For many families, acetaminophen is the first thing reached for when a child spikes a fever or a headache won't quit, and used as directed it is a dependable part of the medicine cabinet. The trouble usually starts quietly: a cold-and-flu syrup at night, a pain tablet in the morning, and nobody notices that both contain the same ingredient. Too much can injure the liver, and early on a person may feel only mildly unwell or perfectly fine, which is why a suspected overdose needs urgent care even before symptoms appear. Knowing what is in each box, and keeping track over a sick day, is most of what keeps this familiar medicine safe.

Everyday exposure: where you meet it and how much

Acetaminophen, called paracetamol in most of the world, is used for pain and fever. It is sold on its own and in many cold, flu, sleep and prescription combination products. That matters, because the main avoidable risk comes from taking two products that both contain it. [1,2]

Health Canada says adults should not take more than 4,000 mg in 24 hours from all sources unless a health professional advises otherwise. People with liver disease, or who drink three or more alcoholic drinks a day, may need a lower limit. Follow the label of the actual product, and the dose for children by weight or age. [1,2]

Known and suspected harms

Evidence labels are editorial summaries, not individual risk predictions: established means recognized under the stated conditions; probable means a likely contribution with uncertainty; possible means limited evidence; disputed means assessors disagree. These labels do not describe how common an effect is.

• Established — liver injury from taking too much: MedlinePlus warns that too much acetaminophen can damage the liver, sometimes badly enough to need a transplant or cause death. Health Canada says acetaminophen is a leading cause of acute liver failure, and that overdoses lead to about 4,500 hospital stays a year in Canada, about 16% of them accidental. Early symptoms can be mild or absent, so suspected overdose needs urgent care even if the person feels well. [1,2]
• Established — rare serious skin and allergic reactions: MedlinePlus lists red, peeling or blistering skin, rash, hives, swelling and trouble breathing as reasons to stop and get medical help. [1]
• Disputed — use in pregnancy causes autism or ADHD: in September 2025 FDA described an association reported in some studies and started a label change, while saying a causal link had not been established. EMA says the evidence does not show that paracetamol causes autism, and that its advice on use in pregnancy is unchanged. ACOG continues to regard it as an appropriate option in pregnancy when needed. Anyone pregnant should discuss pain or fever treatment with a clinician, because untreated fever also carries risks. [4–6]

Reducing avoidable exposure and harm

Check the active ingredients of every medicine you take at the same time, including night-time and cold remedies. Use a dosing device made for the product, keep track of doses, and do not exceed the daily limit on the label. Ask a pharmacist before use if you have liver disease or drink alcohol regularly. Store medicines where children cannot reach them. If too much has been taken, call a poison centre or emergency services right away. [1,2]

What it is

Acetaminophen is a pain reliever and fever reducer. Its CAS number is 103-90-2. It is a different kind of medicine from nonsteroidal anti-inflammatory drugs, so the cautions for those medicines do not transfer directly, and vice versa. [1,7]

What it does and why it is used

It relieves mild to moderate pain, such as headache, muscle ache, toothache and period pain, and lowers fever. It is used by adults and children, in tablets, capsules, liquids, suppositories and combination products. [1]

Regulatory status and health context

Canada

In Canada acetaminophen is available without a prescription. Health Canada's consumer page sets out the 4,000 mg daily limit for adults and the liver-injury risks above. It has also announced a limit of 325 mg of acetaminophen per unit in prescription combination products. [2,3]

United States

In the United States acetaminophen is sold over the counter and in prescription combinations. FDA's September 2025 announcement on pregnancy said it was starting a label change to reflect a possible association, while stating that a causal relationship had not been established and that some studies did not find one. [1,4]

European Union

EMA reviewed the same question and concluded that available evidence does not show that paracetamol use in pregnancy causes autism. Its advice is that paracetamol can be used in pregnancy when needed, at the lowest effective dose for the shortest time. [5]

Environmental notes

MedlinePlus advises using a medicine take-back program and not flushing acetaminophen. Ask a pharmacist about local return options. The sources used here do not give enough environmental data to rate its aquatic risk. [1]

Quick facts

• CAS: 103-90-2. [7]
• Other names: paracetamol, APAP. [7]
• Purpose: pain relief and fever reduction. [1]
• Adult maximum in Canada: 4,000 mg in 24 hours from all sources, unless advised otherwise. [2]
• Main avoidable risk: accidental double-dosing across products. [1,2]

Sources

All URLs were fetched on 2026-11-10. Source publication dates differ from this draft's review date.

1. MedlinePlus: Acetaminophen.
2. Health Canada: Acetaminophen.
3. Health Canada: Notice on limiting the strength of acetaminophen to 325 mg per dosage unit in prescription combination products.
4. FDA: FDA Responds to Evidence of Possible Association Between Autism and Acetaminophen Use During Pregnancy.
5. EMA: Use of paracetamol during pregnancy unchanged in the EU.
6. ACOG: Acetaminophen use in pregnancy and neurodevelopmental outcomes.
7. PubChem PUG REST: acetaminophen synonyms.