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The Food and Drug Administration (FDA) says physicians should stop prescribing combination drugs with more than 325 milligrams (mg) of acetaminophen.

Acetaminophen is available in prescription pain relieving medications like Percocet and Vicodin, in which it is combined with opiods, as well as over the counter (OTC) drugs like Tylenol. The FDA says there is no evidence that taking more than 325mg in a combination pill provides any additional benefit, and too much acetaminophen puts people at risk of severe liver injury. “Many consumers are often unaware that many products (both prescription and OTC) contain acetaminophen, making it easy to accidentally take too much,” the agency said in its statement.

The FDA is now asking doctors not to prescribe pain relievers that contain more than 325mg of acetaminophen, since people may take these drugs along with OTC medications and expose themselves to potentially harmful levels of the medication. In 2011, the agency asked manufacturers of acetaminophen-combined prescription drugs to limit the amount of acetaminophen to no more than 325mg by 2014. More than half have agreed, but medications with higher amounts are still on the market. The FDA says it plans to start withdrawing approval of combination drugs requiring prescriptions that exceed this limit.

For now, the new recommendation to physicians only applies to prescription drugs with acetaminophen, and not to over-the-counter drugs like Tylenol, but the FDA says it will address those in a separate regulatory action. The agency is also recommending that pharmacists who receive prescriptions for drugs with more than the 325mg per dose call the prescribing physician and inform him of the FDA’s new warning.

According to the agency, unintended overdoses with prescription combination drugs involving acetaminophen are responsible for half of acetaminophen-related liver failure in the U.S.