Harvard Women's Health Watch

FDA limits prescription acetaminophen

But be vigilant about over-the-counter acetaminophen, too.

In January 2011, the FDA ordered makers of prescription acetaminophen drugs — mostly acetaminophen-plus-opioid combinations such as Vicodin and Percocet — to put no more than 325 milligrams (mg) of acetaminophen (better known as Tylenol) in each pill or capsule; currently, these combinations may contain as much as 750 mg. Manufacturers were also told to include a "black box" warning (the most serious kind) on product labels highlighting the risk of severe liver injury. Acetaminophen overdose causes most cases of acute liver failure in the United States, and acetaminophen-containing prescription drugs account for nearly half of them. It happens especially when people try to get additional pain relief by taking more of the prescription drug.

Acetaminophen produces a toxic by-product when the liver breaks it down. Normally, this toxin is neutralized by a substance called glutathione, but excess acetaminophen may overwhelm glutathione stores, allowing the toxin to build up and damage the liver. Alcohol can deplete glutathione — one reason you shouldn't take it with acetaminophen. Glutathione levels are also reduced by certain genetic defects, medications, and chemicals. An antidote is available for acetaminophen overdose, and intentional overdoses are usually discovered and treated. But accidental overdoses tend to accumulate over several days and often go unrecognized until the liver is failing.

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