Caffeine Plus Acetaminophen Toxic for Some

Some people may be more vulnerable to this toxic interaction than others, Nelson said. They might include people who take certain antiepileptic medications, such as carbamazepine and phenobarbital, and people who use the alternative remedy St. John's Wort.

These drugs increase levels of the enzyme that produces NAPQI and may produce even more when mixed with acetaminophen and caffeine together, Nelson speculated.

In addition, because alcohol can boost NAPQI production, people who drink a lot may be at increased risk for this toxic interaction, the researcher said. The risk is also increased for people who take drugs that combine acetaminophen and caffeine, used to treat migraines, arthritis and other conditions.

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Still, for most people, there's no reason to panic, since the chances of caffeine and acetaminophen becoming a toxic mixture remains small, Nelson said.

"Almost all people don't need to worry about taking caffeine with acetaminophen," Nelson said. Exceptions might be, " those [people] taking high does of caffeine, high doses of acetaminophen, who are possibly alcoholic and/or are epileptic and take certain anticonvulsive drugs," he said.

More information

For more on acetaminophen, visit the U.S. National Library of Medicine.