Acetaminophen Uses, Dosage, Side Effects, Food Interaction and all others data.

Acetaminophen (paracetamol), also commonly known as Tylenol, is the most commonly taken analgesic worldwide and is recommended as first-line therapy in pain conditions by the World Health Organization (WHO). It is also used for its antipyretic effects, helping to reduce fever. This drug was initially approved by the U.S. FDA in 1951 and is available in a variety of forms including syrup form, regular tablets, effervescent tablets, injection, suppository, and other forms.

Acetaminophen is often found combined with other drugs in more than 600 over the counter (OTC) allergy medications, cold medications, sleep medications, pain relievers, and other products. Confusion about dosing of this drug may be caused by the availability of different formulas, strengths, and dosage instructions for children of different ages. Due to the possibility of fatal overdose and liver failure associated with the incorrect use of acetaminophen, it is important to follow current and available national and manufacturer dosing guidelines while this drug is taken or prescribed.

Animal and clinical studies have determined that acetaminophen has both antipyretic and analgesic effects. This drug has been shown to lack anti-inflammatory effects. As opposed to the salicylate drug class, acetaminophen does not disrupt tubular secretion of uric acid and does not affect acid-base balance if taken at the recommended doses. Acetaminophen does not disrupt hemostasis and does not have inhibitory activities against platelet aggregation. Allergic reactions are rare occurrences following acetaminophen use.

Trade Name Acetaminophen
Availability Rx and/or OTC
Generic Acetaminophen
Acetaminophen Other Names Acenol, Acetaminofén, Acetaminophen, Acétaminophène, APAP, Paracetamol, Paracétamol, Paracetamolum
Related Drugs Buprenex, aspirin, ibuprofen, tramadol, cyclobenzaprine, Paracetamol, naproxen, diclofenac, Tylenol, oxycodone
Weight 500mg
Type Caplet
Formula C8H9NO2
Weight Average: 151.1626
Monoisotopic: 151.063328537
Protein binding

The binding of acetaminophen to plasma proteins is low (ranging from 10% to 25%), when given at therapeutic doses.

Groups Approved
Therapeutic Class
Manufacturer Neros Pharmaceuticals Ltd
Available Country Canada, Nigeria
Last Updated: September 19, 2023 at 7:00 am


Acetaminophen is an analgesic drug used alone or in combination with opioids for pain management, and as an antipyretic agent.

In general, acetaminophen is used for the treatment of mild to moderate pain and reduction of fever. It is available over the counter in various forms, the most common being oral forms.

Acetaminophen injection is indicated for the management of mild to moderate pain, the management of moderate to severe pain with adjunctive opioid analgesics, and the reduction of fever.

Because of its low risk of causing allergic reactions, this drug can be administered in patients who are intolerant to salicylates and those with allergic tendencies, including bronchial asthmatics. Specific dosing guidelines should be followed when administering acetaminophen to children.

Acetaminophen is also used to associated treatment for these conditions: Acute Gouty Arthritis, Acute Musculoskeletal Pain, Allergies, Ankylosing Spondylitis (AS), Arthritis, Chills, Cold, Cold Symptoms, Common Cold, Common Cold/Flu, Cough, Cough caused by Common Cold, Coughing caused by Flu caused by Influenza, Dyskinesia of the Biliary Tract, Dyskinesia of the Urinary Tract, Febrile Convulsions, Febrile Illness Acute, Fever, Fibromyalgia Syndrome, Flu caused by Influenza, Headache, Joint dislocations, Menstrual Distress (Dysmenorrhea), Mild pain, Muscle Inflammation, Muscle Injuries, Muscle Spasms, Musculoskeletal Pain, Nasal Congestion, Neuralgia, Osteoarthritis (OA), Pain, Pollen Allergy, Postoperative pain, Premenstrual cramps, Rheumatoid Arthritis, Rhinopharyngitis, Rhinorrhoea, Severe Pain, Sinusitis, Soreness, Muscle, Spasms, Spastic Pain of the Gastrointestinal Tract, Sprains, Tension Headache, Toothache, Upper Respiratory Tract Infection, Whiplash Syndrome, Acute Torticollis, Mild to moderate pain, Minor aches and pains, Minor pain, Moderate Pain, Airway secretion clearance therapy, Antispasmodic, Bronchodilation

How Acetaminophen works

According to its FDA labeling, acetaminophen's exact mechanism of action has not been fully established - despite this, it is often categorized alongside NSAIDs (nonsteroidal anti-inflammatory drugs) due to its ability to inhibit the cyclooxygenase (COX) pathways. It is thought to exert central actions which ultimately lead to the alleviation of pain symptoms.

One theory is that acetaminophen increases the pain threshold by inhibiting two isoforms of cyclooxygenase, COX-1 and COX-2, which are involved in prostaglandin (PG) synthesis. Prostaglandins are responsible for eliciting pain sensations. Acetaminophen does not inhibit cyclooxygenase in peripheral tissues and, therefore, has no peripheral anti-inflammatory effects. Though acetylsalicylic acid (aspirin) is an irreversible inhibitor of COX and directly blocks the active site of this enzyme, studies have shown that acetaminophen (paracetamol) blocks COX indirectly. Studies also suggest that acetaminophen selectively blocks a variant type of the COX enzyme that is unique from the known variants COX-1 and COX-2. This enzyme has been referred to as COX-3. The antipyretic actions of acetaminophen are likely attributed to direct action on heat-regulating centers in the brain, resulting in peripheral vasodilation, sweating, and loss of body heat. The exact mechanism of action of this drug is not fully understood at this time, but future research may contribute to deeper knowledge.


LD50 = 338 mg/kg (oral, mouse); LD50 = 1944 mg/kg (oral, rat)

Overdose and liver toxicity

Acetaminophen overdose may be manifested by renal tubular necrosis, hypoglycemic coma, and thrombocytopenia. Sometimes, liver necrosis can occur as well as liver failure. Death and the requirement of a liver transplant may also occur. Metabolism by the CYP2E1 pathway releases a toxic acetaminophen metabolite known as N-acetyl-p-benzoquinoneimine(NAPQI). The toxic effects caused by this drug are attributed to NAPQI, not acetaminophen alone.


Long-term studies in mice and rats have been completed by the National Toxicology Program to study the carcinogenic risk of acetaminophen. In 2-year feeding studies, F344/N rats and B6C3F1 mice consumed a diet containing acetaminophen up to 6,000 ppm. Female rats showed evidence of carcinogenic activity demonstrated by a higher incidence of mononuclear cell leukemia at doses 0.8 times the maximum human daily dose (MHDD). No evidence of carcinogenesis in male rats (0.7 times) or mice (1.2 to 1.4 times the MHDD) was noted. The clinical relevance of this finding in humans is unknown.


Acetaminophen was not found to be mutagenic in the bacterial reverse mutation assay (Ames test). Despite this finding, acetaminophen tested positive in the in vitro mouse lymphoma assay as well as the in vitro chromosomal aberration assay using human lymphocytes. In published studies, acetaminophen has been reported to be clastogenic (disrupting chromosomes) when given a high dose of 1,500 mg/kg/day to the rat model (3.6 times the MHDD). No clastogenicity was observed at a dose of 750 mg/kg/day (1.8 times the MHDD), indicating that this drug has a threshold before it may cause mutagenesis. The clinical relevance of this finding in humans is unknown.

Impairment of Fertility

In studies conducted by the National Toxicology Program, fertility assessments have been performed in Swiss mice in a continuous breeding study. No effects on fertility were seen.

Use in pregnancy and nursing

The FDA label for acetaminophen considers it a pregnancy category C drug, meaning this drug has demonstrated adverse effects in animal studies. No human clinical studies in pregnancy have been done to this date for intravenous acetaminophen. Use acetaminophen only when necessary during pregnancy. Epidemiological data on oral acetaminophen use in pregnant women demonstrate no increase in the risk of major congenital malformations. While prospective clinical studies examining the results of nursing with acetaminophen use have not been conducted, acetaminophen is found secreted in human milk at low concentrations after oral administration. Data from more than 15 nursing mothers taking acetaminophen was obtained, and the calculated daily dose of acetaminophen that reaches the infant is about 1 to 2% of the maternal dose. Caution should be observed when acetaminophen is taken by a nursing woman.

Food Interaction

  • Avoid alcohol. Alcohol may increase the risk of hepatotoxicity.
  • Take with or without food. The absorption is unaffected by food.

Acetaminophen Alcohol interaction


Chronic, excessive consumption of alcohol may increase the risk of acetaminophen-induced hepatotoxicity, which has included rare cases of fatal hepatitis and frank hepatic failure requiring liver transplantation.

The proposed mechanism is induction of hepatic microsomal enzymes during chronic alcohol use, which may result in accelerated metabolism of acetaminophen and increased production of potentially hepatotoxic metabolites.

In general, chronic alcoholics should avoid regular or excessive use of acetaminophen.

Alternative analgesic/antipyretic therapy may be appropriate in patients who consume three or more alcoholic drinks per day.

However, if acetaminophen is used, these patients should be cautioned not to exceed the recommended dosage (maximum 4 g/day in adults and children 12 years of age or older).

Acetaminophen Disease Interaction

Major: alcoholism, liver diseaseModerate: PKU

Volume of Distribution

Volume of distribution is about 0.9L/kg. 10 to 20% of the drug is bound to red blood cells. Acetaminophen appears to be widely distributed throughout most body tissues except in fat.

Elimination Route

Acetaminophen has 88% oral bioavailability and reaches its highest plasma concentration 90 minutes after ingestion. Peak blood levels of free acetaminophen are not reached until 3 hours after rectal administration of the suppository form of acetaminophen and the peak blood concentration is approximately 50% of the observed concentration after the ingestion of an equivalent oral dose (10-20 mcg/mL).

The percentage of a systemically absorbed rectal dose of acetaminophen is inconsistent, demonstrated by major differences in the bioavailability of acetaminophen after a dose administered rectally. Higher rectal doses or an increased frequency of administration may be used to attain blood concentrations of acetaminophen similar to those attained after oral acetaminophen administration.

Half Life

The half-life for adults is 2.5 h after an intravenous dose of 15 mg/kg. After an overdose, the half-life can range from 4 to 8 hours depending on the severity of injury to the liver, as it heavily metabolizes acetaminophen.


Adults: 0.27 L/h/kg following a 15 mg/kg intravenous (IV) dose. Children: 0.34 L/h/kg following a 15 mg/kg intravenous (IV dose).

Elimination Route

Acetaminophen metabolites are mainly excreted in the urine. Less than 5% is excreted in the urine as free (unconjugated) acetaminophen and at least 90% of the administered dose is excreted within 24 hours.

Innovators Monograph

You find simplified version here Acetaminophen


What is Acetaminophen used for?

Acetaminophen is used to relieve mild to moderate pain from headaches, muscle aches, menstrual periods, colds and sore throats, toothaches, backaches, and reactions to vaccinations (shots), and to reduce fever.

How safe is Acetaminophen?

When used as directed, taking Acetaminophen is generally safe and effective.

How does Acetaminophen work?

Acetaminophen relieves pain by elevating the pain threshold, that is, by requiring a greater amount of pain to develop before a person feels it. It reduces fever through its action on the heat-regulating center of the brain.

What are the common side effects of Acetaminophen?

Common side effects of Acetaminophen are include;

  • nausea,
  • stomach pain,
  • loss of appetite,
  • itching,
  • rash,
  • headache,
  • dark urine,
  • clay-colored stools,
  • or jaundice (yellowing of skin or eyes).

Is Acetaminophen safe during pregnancy?

Acetaminophen as one of the only safe pain relievers for pregnant individuals during pregnancy.

Is Acetaminophen safe during breastfeeding?

Acetaminophen are safe to use when breastfeeding.

Can I drink alcohol with Acetaminophen?

Mixing Acetaminophen and alcohol can potentially lead to liver damage. Rarely, liver damage can be severe or even life-threatening.

Can I drive after taking Acetaminophen?

You should know that this medication may make you drowsy. Do not drive a car or operate machinery until you know how this medication affects you. you should know that Acetaminophen and codeine may cause dizziness, lightheadedness, and fainting when you get up too quickly from a lying position.

How often can I take Acetaminophen?

Take every 4 to 6 hours, as needed, up to 4 times in a 24-hour period.

How do I take Acetaminophen?

Take Acetaminophen exactly as directed on the prescription or package label.

How much Acetaminophen can I take daily?

The usual dose is 325 mg to 650 mg. Take every 4 to 6 hours, as needed, up to 4 times in a 24-hour period. The maximum dose may vary from 3,000 mg to 4,000 mg, but do not take more than 4,000 mg in a 24-hour period.

How long does Acetaminophen take to work?

It usually takes about 45 minutes for oral, liquid, or tablet Acetaminophen to start working. The oral disintegrating tablets start to work in about 20 minutes.

What is the half life of Acetaminophen?

The Acetaminophen half-life was 5.4 hours (range, 0.8-119.7 hours).

How long can I take Acetaminophen?

Don't take Acetaminophen for more than 10 days in a row unless you've been instructed to do so by your doctor.

Who should not take Acetaminophen?

You should not take Acetaminophen if you are allergic to it, or if you take other medications that contain acetaminophen. Ask a doctor or pharmacist if this medicine is safe to use if you've ever had cirrhosis of the liver, or if you drink alcohol daily.

What happens if I miss a dose?

Since Acetaminophen is taken as needed, you may not be on a dosing schedule. If you are taking the medication regularly, take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention. An overdose of acetaminophen can be fatal. The first signs of an Acetaminophen overdose include loss of appetite, nausea, vomiting, stomach pain, sweating, and confusion or weakness. Later symptoms may include pain in your upper stomach, dark urine, and yellowing of your skin or the whites of your eyes.

Should I stop taking Acetaminophen?

It is suggested that you stop taking Acetaminophen and talk with your doctor if: You still feel pain after 10 days (adult) or 5 days (children) You still have a fever after 3 days. Your symptoms get worse, or you feel new symptoms.

Can Acetaminophen affects my heart ?

It is not known to increase risks of heart attack, heart failure, or stroke.

Can Acetaminophen affect my kidneys?

Acetaminophen broken down/metabolized almost completely by the liver, so the kidneys hardly do any of the work and are not affected by it. Acetaminophen is safe for the kidneys.

Can Acetaminophen affects my liver?

Acetaminophen toxicity can quickly lead to liver damage. Liver damage associated with Acetaminophen use sends thousand of Americans to the hospital each year.
*** Taking medicines without doctor's advice can cause long-term problems.