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.