Explains Dr. Moore, “Acetaminophen has always been thought to have no gastric-irritating effects, just liver toxicity. This article points out that at extremely high doses of 3 grams per day, it can also cause GI blood loss, as NSAIDs [nonsteroidal anti-inflammatory drugs] have been known for.”

Such a high dose is easy to reach if you’re not careful. Each tablet of Tylenol Arthritis Pain, for example, contains 650 mg of acetaminophen; taking 5 tablets a day exceeds three grams, or 3,000 mg.

The researchers point out that additional research is needed to confirm their findings. “It would seem, however, that further study of the gastrointestinal safety of [acetaminophen] and the combination of [acetaminophen] and NSAID is justified, especially given the widespread use of these drugs and the ability to self-medicate at the doses used in this study,” write the researchers.

Elaine Husni, MD, director of the arthritis and musculoskeletal center at the Cleveland Clinic and vice chair of the department of rheumatologic and immunologic diseases, applauds research in this area – which she says is rare and much needed.

“More needs to be done, because this is what everyone is taking,” Dr. Husni says. “The thing your grandmother could buy at drug stores could equally have side effects and needs to be monitored, and that’s an important message.”

So, what does that mean for consumers? Tell your doctor about all medications you take, including over-the-counter drugs, plus when and how often you take them.

“If we don’t know what other drugs you are taking, we won’t be able to warn you or look out for additional side effects,” Dr. Husni says. She notes that many patients don’t realize they should mention the OTC drugs they are taking to their doctors.

But Miller softens the message some. “There’s a little potential danger with anything. I think it’s worth reminding people you should always use the lowest dose for the minimum period possible if you can, and don’t use any medication for a long time or at high doses without letting your doctor know what you are doing.”

Miller says he still thinks acetaminophen – in moderate doses – is a good first choice treatment for most OA patients and has the best safety profile overall. But he says this study clearly warns of the problems with combining over-the-counter medications. He says patients should take only one over-the-counter medicine at a time.

Dr. Moore agrees. “The take home for patients is, they should know the medication and the dosage they are taking, and in most cases not exceed 1 to 2 grams [1,000 mg to 2,000 mg] of acetaminophen a day, and lower doses NSAIDs if possible,” he says. “All pain and anti-inflammatory medications should be followed with blood work every four months to insure [there’s] no development of toxicity.”