Acetaminophen (Tylenol) is widely recommended for the relief of back pain and the pain of knee and hip arthritis. But a systematic review of randomized trials has found that it works no better than a placebo.

Australian researchers reviewed three randomized trials that compared acetaminophen with a placebo for the relief of spinal pain, and 10 trials that compared their use for easing the pain of osteoarthritis. All together, the analysis included 5,366 patients. Acetaminophen was given orally in doses between 3,000 and 4,000 milligrams a day, except for one study in which a dose of 1,000 milligrams was administered intravenously.

The review, published online in BMJ, found high quality evidence that Tylenol is ineffective in treating low back pain or disability. It also found evidence that the drug quadruples the risk of an abnormal liver function test, but the clinical significance of that finding is unclear.

The studies of pain from knee and hip arthritis found a small but clinically insignificant short-term pain-relief effect for acetaminophen compared with a placebo.

Clinical guidelines from medical groups typically recommend acetaminophen for pain relief, but “the American guidelines were published in 2007, when the evidence was weaker,” said the senior author, Manuela L. Ferreira, an associate professor at the George Institute for Global Health in Sydney. “This new evidence - the highest quality evidence from papers all over the world — shows that it is time to review the recommendations on acetaminophen.”

The lead author, Gustavo C. Machado, a Ph.D. candidate at the George Institute, added that patients should talk to their doctors and “discuss what are the best treatment options, and what are the harms and benefits. And they should be aware that this review shows that acetaminophen should not be recommended as a first line analgesic for these conditions.”

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By Nicholas Bakalar