Acetaminophen — the active ingredient in the popular painkiller Tylenol — has been shown to have negative psychological effects and may blunt positive emotions.

A new study of people who took acetaminophen reported less strong emotions — particularly less joy — when they viewed emotionally compelling photos, compared to those who took inactive placebos.

The Ohio State University research is the first to document psychological side effects in people who take acetaminophen.

"This means that using Tylenol or similar products might have broader consequences than previously thought," said Geoffrey Durso, lead author of the study and an OSU doctoral student in social psychology. "Rather than just being a pain reliever, acetaminophen can be seen as an all-purpose emotion reliever."

The OSU findings, published online in the journal Psychological Science, are based studies of college students — half of whom took acetaminophen and half who took an identical-looking placebo before viewing 40 photographs designed to elicit positive and emotional responses.

The results showed that participants who took the painkiller rated all the photographs less extremely than did those who took the placebo — meaning they didn’t feel the same highs or lows as those who took placebos.

Acetaminophen is the most common drug ingredient in the United States, found in more than 600 medicines, according to the Consumer Healthcare Products Association, a trade group.

Each week about 23 percent of American adults (about 52 million people) use a medicine containing acetaminophen, the CHPA reports.