Acetaminophen: Indications, Dosing & Contraindications

Acetaminophen is an analgesic (pain reliever) and antipyretic (fever reducer) indicated for mild to moderate pain and fever associated with colds or the flu. It may also be recommended to help manage back pain, toothache, osteoarthritis, or menstrual cramps.

Acetaminophen is available without a prescription at pharmacies and drugstores as the generic "acetaminophen" and under the brand name Tylenol, among others. It comes as both a pill and an oral solution.

Acetaminophen is approved for use in children, adults, and pregnant people and should be taken under the guidance of a doctor or other healthcare professional. Following the recommended dosing instructions is essential to avoid potentially serious liver complications like drug-induced hepatitis and liver failure.

Indications for use

Acetaminophen is typically indicated for the treatment of:

• Fever;
• Headache;
• Muscle pain;
• Toothache;
• Osteoarthritis;
• Period cramps;
• Low back pain;
• Sinusitis.

Acetaminophen can also help relieve body aches and malaise associated with colds or the flu.

While acetaminophen is available over-the-counter (without a prescription), it should be taken only as recommended by a doctor or other healthcare professional to help prevent side effects and overdose that can cause liver toxicity.

Dosing instructions

Acetaminophen is an oral medication (taken by mouth) that can be taken before or after a meal and starts working within 15 to 30 minutes.

A missed dose should be taken as soon as the person remembers, with the next scheduled dose adjusted based on the most recent dose, and so on. Never take a double dose to make up for a missed dose.

Dosing varies based on the formulation, which include:

1. Liquid acetaminophen 

Acetaminophen 160 mg/mL is indicated for babies and children under 12 years of age. Babies under 12 weeks old should not be given acetaminophen unless advised by a doctor.

The following table provides recommended doses of liquid acetaminophen based on weight:

While both Infant's Tylenol and Children's Tylenol contain the same concentration of acetaminophen (160 mg/mL), Infant's Tylenol comes with a syringe that may be more suitable for children under 2–3 years of age. Children's Tylenol comes with a measuring cup and is recommended for children 2–11 years of age.

Use the provided syringe or measuring cup to carefully measure out the dose and be sure to shake the bottle well before use.

The maximum daily dose of liquid acetaminophen is 50 to 75 mg per kg of body weight given in 5 divided doses over a period of 24 hours. Doses should not be given less than 4 to 6 hours apart. Dosing instructions should be confirmed with a pediatrician.

2.  Acetaminophen tablets

Acetaminophen oral tablets can be taken as directed according to the strength of the medication:

• Acetaminophen 80 mg (chewable tablets): 80 mg acetaminophen chewable tablets are dosed based on weight, which is generally 10-15 mg/kg/dose (not to exceed 5 doses in 24 hours). Make sure to confirm the dose with a pharmacist or your child's pediatrician;
• Acetaminophen 160 mg (Children's Tylenol Chewables): acetaminophen chewable tablets are indicated for children ages 2 and up who weigh more than 24 lb. Make sure to confirm the dose with a pharmacist or your child's pediatrician;
• Acetaminophen 325 mg (Regular Strength Tylenol): for children ages 6–11: 1 tablet every 4 to 6 hours (not to exceed 5 tablets in 24 hours); for adults and children 12 years of age and older: 2 tablets every 4 to 6 hours while symptoms last (not to exceed 10 tablets in 24 hours unless directed by a doctor);
• Acetaminophen 500 mg (Extra Strength Tylenol): 1 to 2 tablets every 4 to 6 hours, or as recommended by a healthcare provider, for a maximum of 8 tablets in a 24-hour period;
• Acetaminophen 650 mg (Tylenol 8 HR Arthritis Pain): 2 tablets every 6 hours while symptoms last, not to exceed 6 tablets in 24 hours.

The maximum dose for children and adults 12 years of age and older is 4000 mg per day. Doses should be given at least 4 to 6 hours apart and should not exceed 1000 mg per dose.

Duration of treatment will depend on how long it takes symptoms to resolve. Acetaminophen should not be taken for more than 10 days in a row (or more than 3 days in a row in the case of fever).

Side effects

Acetaminophen is a medication that is considered safe when taken as prescribed at the recommended doses.

Side effects like nausea, vomiting, constipation, body itching or redness, or allergic reactions can occur.

Can acetaminophen cause liver failure?

Taking acetaminophen at higher-than-recommended doses can severely affect the liver, leading to potentially life threatening conditions like drug-induced hepatitis and even liver failure.

People with symptoms of acetaminophen overdose, such as nausea, vomiting (which may contain blood), excessive sweating, pale skin, loss of appetite, abdominal pain, full-body itching, or yellow skin and eyes, should stop taking acetaminophen and be seen immediately at the emergency department. 

Maximum doses

To avoid complications, it is important to adhere to the maximum daily doses of acetaminophen, which are:

• Children under 12 years of age: 50 to 75 mg of liquid acetaminophen (160 mg/5 mL) per kg of body weight divided into 5 doses given every 4 to 6 over a period of 24 hours;
• Adults and children 12 years of age and older: 4000 mg per day, which corresponds to 12 regular strength (325 mg) tablets or 8 extra strength (500 mg) tablets in a 24 hour period. Doses should be taken every 4 to 6 hours and should not exceed 1000 mg per dose.

Dosing should always be determined by a healthcare provider, especially in the case of children under 2 years of age or weighing less than 24 lb (11 kg).

Contraindications to use

Acetaminophen should not be taken by people with an allergy to acetaminophen or any components of its formula.

It is also contraindicated in cases of heavy alcohol use, severe liver problems, and in people taking other medications containing acetaminophen to avoid an overdose that can lead to liver toxicity, liver failure, or drug-induced hepatitis.

Use in pregnancy

Acetaminophen is an analgesic approved for use during pregnancy and should be taken only as recommended by an OBGYN or midwife at the lowest effective dose. The maximum daily dose during pregnancy should not exceed 3000 mg when possible, in contrast to the 4000 mg maximum dose for non-pregnant adults.