Mixing large doses of both acetaminophen painkiller and caffeine may increase risk of li...(current finding. People should be i...)

People should be informed about this potentially harmful interaction, Nelson says. The bottom line is that you dont have to stop taking acetaminophen or stop taking caffeine products, but you do need to monitor your intake more carefully when taking them together, especially if you drink alcohol.

Nelson points out that the bacteria used in the study were exposed to megadoses of both acetaminophen and caffeine, much higher than most individuals would normally consume on a daily basis. Most people would similarly need to consume unusually high levels of these compounds together to have a dangerous effect, but the toxic threshold has not yet been determined, he says.

Certain groups may be more vulnerable to the potentially toxic interaction than others, Nelson says. This includes people who take certain anti-epileptic medications, including carbamazepine and phenobarbital, and those who take St. Johns Wort, a popular herbal supplement. These products have been shown to boost levels of the enzyme that produces the toxic liver metabolite NAPQI, an effect that will likely be heightened when taking both acetaminophen and caffeine together, he says.

Likewise, people who drink a lot of alcohol may be at increased risk for the toxic interaction, Nelson says. Thats because alcohol can trigger the production of yet another liver enzyme that produces the liver toxin NAPQI. The risks are also higher for those who take large amounts of medications that combine both acetaminophen and caffeine, which are often used together as a remedy for migraine headaches, arthritis and other conditions.

The researchers are currently studying the mechanism by which this toxic interaction occurs and are considering human studies in the future, they say. The National Institutes of Health funded the initial animal and bacterial studies.

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