Frequent and long-term users of acetaminophen may face an increased risk of blood cancer, according to new research.

In a study published this week by the Journal of Clinical Oncology, researchers from the University of Washington looked at data on nearly 65,000 older men and women who participated in a study called Vitamins and Lifestyle (VITAL) in 2000 to 2002. The analysis found that by 2008, those who used acetaminophen for at least four days per week for four years were twice as likely to have developed some form of blood cancer.

Researchers identified 577 cases of blood cancer out of the 64,839 people ages 50 to 76 who participated in the original study. The blood malignancies included non-Hodgkin lymphomas, plasma cell disorders and myeloid neoplasms.

The only painkiller they found to be associated with an increased blood cancer risk was acetaminophen. Chronic use of aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) did not appear to have the same correlation.

The researchers stressed that the study’s findings did not show causality and pointed out that the actual risk of blood cancer with acetaminophen use was very low.

Acetaminophen, the generic name for Tylenol, is a pain killer and anti-inflammatory medication found in a number of over-the-counter and prescription drugs. In recent years, federal regulators have become concerned over the frequency of its use in a variety of medications. Overuse of the drug could lead to liver injury and other health problems, according to the FDA.

Earlier this year the FDA placed new limits on acetaminphen’s use in other, more powerful, painkillers. Drugs affected by the new acetaminophen limits include Vicodin (acetaminophen and hydrocodone), Percocet (acetaminophen and oxycodone), and Tylenol with Codeine (acetaminophen and codeine).

Tags: Acetaminophen, Aspirin, Blood, Cancer, Codeine, Liver Injury, Lymphoma, Oxycodone, Percocet, Tylenol, Vicodin, Washington

