Coffee and flue do not match. Mixing large amounts of caffeine with acetaminophen (paracetamol), one of the most common painkillers used in the US and Europe could harm your liver, as found by a new research.

The danger does not come only from caffeinated dinks combined with the drug, but also from medications mixing caffeine and acetaminophen against headaches, menstrual discomfort, arthritis and other issues. Paracetamol is also used for reducing the risk of ovarian cancer, but long-term use can rise the risk of kidney failure, high blood pressure and strokes. The harmful (and potentially lethal) effect of mixing alcohol with acetaminophen was already well-known.

The team led by Dr. Sid Nelson at the University of Washington in Seattle checked the effects of acetaminophen and caffeine on E. coli bacterium strain containing a key human enzyme involved in the liver's detoxification action against many drugs. The caffeine was found to triple the quantity of a toxic byproduct, N-acetyl-p-benzoquinone imine (NAPQI), produced by the enzyme while degrading the acetaminophen.

NAPQI also caused liver damage and failure in toxic alcohol-acetaminophen interactions. The same team had found that high doses of caffeine can boost liver damage in rats that have been administered acetaminophen. "People should be informed about this potentially harmful interaction. The bottom line is that you don't 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.", said Nelson.

The tested bacteria received 'megadoses' of both paracetamol and caffeine, much higher than humans usually consume each day, corresponding to about 20-30 cups of coffee. "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. Certain groups may be more vulnerable to the potentially toxic interaction than others. This includes people who take certain anti-epileptic medications, including carbamazepine and phenobarbital, and those who take St. John's 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", Nelson explained.