By Pat Anson, PNN Editor

Acetaminophen is the most widely used over-the-counter pain reliever in the world — the active ingredient in Tylenol, Excedrin, and hundreds of pain medications. The U.S. Centers for Disease Control and Prevention considers acetaminophen a “first-line” treatment for low back pain, osteoarthritis and migraine.

But a comprehensive review published in the Medical Journal of Australia found little or no evidence to support the use acetaminophen for most pain conditions. Researchers at the University of Sydney analyzed 36 studies involving over 19,000 people and concluded that the pain-relieving benefits of acetaminophen – known as paracetamol outside the U.S. -- are modest, at best.

“For most conditions, evidence regarding the effectiveness of paracetamol is insufficient for drawing firm conclusions. Evidence for its efficacy in four conditions was moderate to strong, and there is strong evidence that paracetamol is not effective for reducing acute low back pain,” wrote senior author Christopher Maher, PhD, a professor at the Sydney School of Public Health.

Maher and his colleagues looked at 44 pain conditions often treated with paracetamol, and could find only four for which there is high-quality evidence:

• Knee and hip osteoarthritis

• Tension headache

• Perineal pain after childbirth

• Craniotomy

Evidence for the other 40 pain conditions was low quality or inconclusive, including:

• Acute and chronic low back pain

• Major surgery

• Dental surgery

• Migraine

• Rheumatoid arthritis

• Hip fracture

• Cancer pain

• Neuropathic pain

“While paracetamol is widely used, its efficacy in relieving pain has been established for only a handful of conditions, and its benefits are often modest. Although some trials have evaluated regimens that may have underestimated its utility, the clinical application of paracetamol is primarily guided by low quality evidence, at best,” researchers said.  

A 2015 study in the British Medical Journal also found that paracetamol was ineffective for low back pain and provided little benefit to people with osteoarthritis.

In recent years, some U.S. hospitals have started using paracetamol as an alternative to opioids for post-operative pain, a practice not supported by the Australian study.

One limitation of the University of Sydney review is that most of the studies that were evaluated only used a single dose of paracetamol, which does not reflect its typical use.  Perhaps for that reason, researchers found that adverse events were similar for patients receiving paracetamol or a placebo.

Over 50 million Americans use paracetamol (acetaminophen) each week to treat pain and fever. Long-term use has long been associated with liver, kidney, heart and blood pressure problems. Acetaminophen overdoses are involved in about 500 deaths and over 50,000 emergency room visits in the U.S. annually.