Acetaminophen is a pain reliever and fever reducer that is among the most widely used medicines in the United States. The Food and Drug Administration (FDA) is now issuing a warning about a rare but serious skin reaction that could occur from the use of the medication.

Although considered rare, possible reactions to the use of the drug include three serious skin diseases with symptoms that include rash, blisters and, in the worst of cases, widespread damage to the surface of the skin. The FDA is now warning that if you are currently taking the medication and develop a rash or any other skin reaction, stop use immediately and seek medical attention as soon as possible.

Acetaminophen has been used for decades by millions of people and is the generic name for a common active ingredient found in numerous prescription and over-the-counter medicines. Tylenol is among one of the most common brand names, but generic forms are sold under a variety of different names. It is also used in combination with a variety of other drugs, including opioids for pain and medications that treat colds, coughs, allergies headaches and insomnia.

“This new information is not intended to worry consumers or health care professionals, nor is it meant to encourage them to choose other medications,” says Sharon Hertz, M.D., deputy director of FDA’s Division of Anesthesia, Analgesia and Addiction. “However, it is extremely important that people recognize and react quickly to the initial symptoms of these rare but serious, side effects, which are potentially fatal.”

Other drugs used to treat pain and fever, including nonsteroidal anti-inflammatory drugs like ibuprofen and naproxen, already carry warnings about the risk of skin reactions. Advil and Motrin are among the most common brand names for medications that include ibuprofen as the active ingredient. Aleve and Midol are the most common brand names for medications that include naproxen as their primary active ingredient.

The FDA is now requiring a warning about these skin reactions to be added to the labels of all prescription drugs containing acetaminophen. They will also work with drug manufacturers to get the same warning added to the labels of over-the-counter drugs containing the active ingredient.

On over-the-counter medicines, the word “acetaminophen” is printed on the front of the packaging and the drug facts label, under active ingredients. On prescription medicines, it may be spelled out on the label or be printed with a shortened abbreviation for the ingredient such as “APAP,” “acet,” “acetamin” or “acetaminoph.”