Acetaminophen is a medication that relieves mild to moderate pain and reduces fever. It is often used by patients who cannot tolerate anti-inflammatory drugs such as aspirin.

Unlike those drugs, acetaminophen does not significantly reduce the stiffness, redness and inflammation often associated with diseases such as arthritis. Yet it can help treat a wide range of conditions from headaches to whiplash to back pain.

Scientists are unsure exactly how acetaminophen works to relieve pain. However, it is believed that the drug may increase a patient’s pain threshold by blocking pain centers in the central nervous system. In some cases, acetaminophen therapy is combined with opioids or other drugs. This combination can enhance the painkilling effect of the medication.

Acetaminophen is available as a standard tablet, chewable tablet, capsule, liquid, drop, suppository or granule that can be dissolved in water. Dosage levels are adjusted for age to limit the chance of side effects, which include anemia, skin rash and other conditions.

Though acetaminophen is often a safe and effective painkiller, it can be dangerous when not taken at the proper dosage or if a person has certain medical conditions. Overdose is a leading cause of liver failure. Patients who have concerns, such as those who suspect they may be allergic, have a history of alcohol abuse, or have had liver or kidney disorders, should first talk with a physician before taking acetaminophen.

Acetaminophen is a medication used to relieve mild to moderate pain. It can also be used as a fever reducer, but it does not significantly reduce the stiffness, redness and inflammation associated with diseases such as arthritis.

Acetaminophen first appeared as an over–the–counter drug in 1954. It belongs to the drug family called analgesics, and is often used as a painkiller by patients who cannot tolerate nonsteroidal anti–inflammatory drugs (NSAIDs) such as aspirin, ibuprofen or naproxen.

Scientists are unsure exactly how acetaminophen works to relieve pain. However, it is believed that the drug may increase a patient’s pain threshold by blocking pain centers in the central nervous system.

In some cases, acetaminophen therapy is combined with opioids such as codeine. This combination can enhance the medication’s painkilling effect. In other cases, acetaminophen is combined with aspirin.

Acetaminophen is available as a standard tablet, chewable tablet, capsule, liquid, drop, suppository or granule that can be dissolved in water. Dosage levels depend on age. The degree of painkilling and fever–reducing effect is similar to that of equivalent doses of aspirin.

Although acetaminophen is available without a prescription, a physician may have special instructions for how to take the drug. Patients should always take it exactly as directed. Acetaminophen overdose (either by itself or as part of a combination of drugs) is common when compared to other medications. It is a leading cause of liver failure. Forty to 50 percent of U.S. cases of acute liver failure are due to overdose of acetaminophen, and nearly half of those overdoses are unintentional, researchers at the University of Michigan reported in 2006.

The National Institutes of Health (NIH) cautions about two forms of kidney disease that can result from use of over-the-counter pain drugs including acetaminophen and NSAIDs:

• Sudden-onset acute kidney failure can occur in people with risk factors including old age, chronic kidney disease, systemic lupus erythematosus or alcohol abuse.
  
  
• Chronic kidney damage (analgesic nephropathy) can develop in anyone taking these drugs daily over several years.

Patients are advised not to take acetaminophen for more than 10 days (five days for children) to treat pain. If pain persists for longer than this period of time, a physician should be consulted.

Types and differences of acetaminophen

Acetaminophen is available under many store names and other brand names. These include:

Acetaminophen is also an ingredient in many combination drugs. These include mixtures with:

• Opioids, including codeine (Tylenol 3), propoxyphene (Darvocet) or hydrocodone (Anexsia, Bancap, Co-Gesic, Lorcet, Lortab, Maxidone, Vicodin, Zydone), and other strong analgesics such as tramadol (Ultracet)
  
  
• Decongestant, allergy and sleep-aid ingredients, such as pseudoephedrine (Allerest, Benadryl, Dristan, Ornex, Sinarest, Sine-Off, Sinutab, Sudafed, Tylenol) and diphenhydramine (Percogesic, Sominex, Tylenol PM)
  
  
• Cough and cold medicines such as phenyltoloxamine (Percogesic)
  
  
• The barbiturate butalbital, to treat conditions such as tension headaches (Axocet, Bupap, Esgic, Fioricet, Phrenilin)
  
  
• Treatments for menstrual pain, such as pamabrom and pyrilamine (Midol, Pamprin, Women’s Tylenol)
  
  
• Caffeine (Esgic, Excedrin, Fioricet)

Acetaminophen can often be used as a safe alternative to other pain relievers, such as aspirin (which increases the risk of Reye's syndrome in children, a rare but potentially fatal condition). However, patients should inform their physician of certain conditions before taking acetaminophen. These include:

• Allergy to acetaminophen or other drugs, or to foods, preservatives or dyes
  
  
• History of liver disease
  
  
• History of alcohol abuse
  
  
• History of kidney disorders or conditions that can damage the kidneys, including systemic lupus erythematosus, sickle cell anemia and diabetes

Patients with phenylketonuria (PKU), a disorder that can cause brain damage and progressive mental retardation, should not use brands of acetaminophen that contain the artificial sweetener aspartame, which can worsen the condition.

Patients with diabetes may find that acetaminophen can cause them to have false results during glucose (blood sugar) tests. Acetaminophen can also interfere with the results of other medical tests. Patients who have scheduled a medical test should inquire in advance about whether they need to refrain from taking acetaminophen for several days before the test.

Overuse of acetaminophen is a leading cause of liver failure. It is important to use acetaminophen as directed and not to assume that, because it is an over-the-counter drug, more can be taken. A recent study blamed overdose of acetaminophen for up to half the cases of acute liver failure in the United States. Another recent study involving 22 U.S. hospitals found that cases of acute liver failure due to accidental or intentional overdoses of acetaminophen rose from 28 percent to 51 percent between 1998 and 2003.

Acetaminophen is generally gentler on the stomach than aspirin. However, in some patients, acetaminophen can cause upset stomach. To help avoid this problem, patients may be advised to take acetaminophen with meals or milk. It is important to note that caffeine increases the effect of acetaminophen.

Unlike aspirin, acetaminophen does not have antiplatelet effects (platelets are essential for blood clotting) and is not associated with Reye’s syndrome (a rare but potentially fatal condition that affects all organs of the body). However, it can have other adverse health effects. Patients should call their physician immediately if they experience:

• Jaundice. Yellowish discoloration of the whites of the eyes, skin and mucous membranes that may indicate liver damage from toxic doses of acetaminophen.
  
  
• Hypoglycemia. An abnormally low level of glucose (blood sugar). Symptoms include trembling, hunger, headache, confusion, rapid heart rate and blurred vision.
  
  
• Hemolytic anemia. Anemia resulting from the abnormal destruction of red blood cells. Symptoms include chills, fatigue, shortness of breath and rapid heart rate.
  
  
• Skin rash. A change in the skin which affects its appearance or texture.

Patients should consult their physician before taking any additional prescriptions, over–the–counter medications, nutritional supplements or herbal medications. Many over–the–counter drugs contain acetaminophen. Patients should be careful to read the labels of other drugs, as the presence of acetaminophen in these medications may affect their ability to take acetaminophen as a painkiller.

Patients should not combine the use of acetaminophen with nonsteroidal anti–inflammatory drugs (NSAIDs) such as aspirin or ibuprofen. Consumption of alcohol – even in moderate amounts – while using acetaminophen can substantially increase the risk of liver damage, particularly when drinking is done on an empty stomach. Alcohol use activates a process that turns acetaminophen into chemicals that cause liver damage.

Other drugs of particular concern to individuals taking acetaminophen are:

• Antacids. These may delay or decrease the absorption of acetaminophen.
  
  
• Anticoagulants and thrombolytics (drugs that break up blood clots). Acetaminophen may increase the effects of these drugs.
  
  
• Anticonvulsants. The combination of acetaminophen with these drugs may raise the risk of toxic damage to the liver (hepatotoxicity). In particular, the combination of acetaminophen and the newer anticonvulsant lamotrigine may decrease serum lamotrigine levels.
  
  
• Phenothiazine. Large doses of acetaminophen combined with this drug used to treat psychiatric disorders may raise the risk of hypothermia (abnormally low body temperature).
  
  
• Other drugs and supplements, including:
  
  
• • Sulfinpyrazone. A drug used to treat gout that promotes urinary excretion of uric acid. The combination of sulfinpyrazone and acetaminophen can damage the liver.
    
    
  • Watercress. An herb that may inhibit the oxidative metabolism of acetaminophen. Oxidative metabolism is a chemical process in which oxygen is used to make energy from carbohydrates.
    
    
  • Caffeine. May increase the effects of acetaminophen.

Acetaminophen is metabolized by an enzyme in the liver. This is also true of many other medications, including other analgesics, anticonvulsants, antifungal agents, antibiotics and other drugs. As a result, it is easy to overwhelm the liver’s ability to metabolize these agents, which can frequently lead to overdose. Accidental and intentional overdose of acetaminophen are so common that hospital emergency rooms have protocols in place for dealing with these emergencies.

Symptoms of acetaminophen overdose can be similar to the medication’s side effects but are usually more severe. Overdose of acetaminophen can lead to toxicity and even death. Patients should always consult their physician before taking acetaminophen or any other medication.

Symptoms or conditions that may result from acetaminophen overdose include:

• Sweating.
  
  
• Stomach pain, cramps, vomiting or diarrhea.
  
  
• Fever.
  
  
• Anemia.
  
  
• Bluish discoloration of the skin (cyanosis).
  
  
• Irregular heartbeat.
  
  
• Skin eruptions.
  
  
• Seizures.
  
  
• Shock.
  
  
• • Delirium. Temporary state of mental confusion and fluctuating consciousness.
    
    
  • Hepatoxicity. Toxic damage to the liver.
    
    
  • Jaundice. Yellowish discoloration of the whites of the eyes, skin, and mucous membranes.
    
    
  • Methemoglobinemia. Presence of the brownish–red form of hemoglobin known as methemoglobin that progresses to depression of the central nervous system.
    
    
• Coma.

Toxicity due to acetaminophen overdose usually occurs in several stages. The first stage occurs 12 to 24 hours after ingestion. Patients exhibiting any of these symptoms during this stage should contact their physician immediately:

• Loss of appetite (anorexia)
• Excessive perspiration (diaphoresis)
• Nausea or vomiting
• Malaise

Stage two occurs 24 to 48 hours after ingestion, and includes symptoms such as abdominal pain and decreased urine output. In stage three (72 to 96 hours after ingestion), liver toxicity reaches its peak and is accompanied by flu–like symptoms, jaundice, low blood sugar (hypoglycemia), impaired consciousness, kidney failure, heart problems and abnormal clotting. Recovery takes place in stage four, seven to eight days after ingestion.

Overdose is treated by giving the patient ipecac syrup (medication that induces vomiting), activated charcoal (medication that neutralizes poisons that have been swallowed) or gastric lavage (washing out the stomach with sterile water or a salt–water solution). In some cases, the drug may be removed from the body through dialysis, a procedure to remove toxic substances or metabolic wastes from the bloodstream.

Studies have not been performed on the effects of acetaminophen on a developing fetus. However, there are no indications linking use of acetaminophen during pregnancy and birth defects. Nonetheless, pregnant women should not use acetaminophen without first consulting their physician.

Acetaminophen passes into breast milk in low levels but does not appear to hurt infants of mothers who breastfeed.

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about acetaminophen:

1. What kinds of pain can I treat with acetaminophen?
   
   
2. I know acetaminophen relieves pain, but which of my other conditions can it treat?
   
   
3. Is acetaminophen available to me in prescription dosages to treat more substantial pain?
   
   
4. What side effects might I experience when taking acetaminophen?
   
   
5. Is risk of liver damage a cause for concern for me?
   
   
6. How careful do I need to be when using acetaminophen?
   
   
7. Is acetaminophen dangerous to me in high doses?
   
   
8. How often should I take this drug?
   
   
9. What if I miss a dose?
   
   
10. Can I give my child acetaminophen?