New research in mice finds acetaminophen may disrupt heart pathways linked to energy, antioxidants, and protein breakdown.

That daily backache medication you’ve been popping may be doing more harm than good.

A new study suggests that one of the world’s go-to pain pills, acetaminophen, can trigger unhealthy changes in heart tissue—even at standard adult dosages long considered perfectly safe. Acetaminophen is the active ingredient in Tylenol and many other pain killers.

The findings add to growing concerns over the medication’s wide range of potential side effects.

Acetaminophen Disrupts Crucial Heart Processes

Even moderate doses of acetaminophen are associated with potential risks over time, according to a new study that was presented at the American Physiology Summit in Long Beach, California.

Using mice as subjects, researchers administered water containing an acetaminophen dosage equivalent to 500 milligrams per day in adult humans. After seven days, significant changes were observed in the levels of proteins associated with various biochemical pathways crucial for heart function, including energy production, antioxidant usage, and the breakdown of damaged proteins.

The results suggest that even at concentrations typically considered safe for human use, acetaminophen can disrupt numerous signaling pathways within the heart.

“We expected two to three pathways to be altered, but we found over 20 different signaling pathways being affected,” Gabriela Rivera, a doctoral student at the University of California–Davis and the study’s lead author, said in a press release.

Acetaminophen had been previously thought to carry a low risk of harmful side effects even when used as directed. This study helps with understanding its effects, which already include a risk of gastrointestinal problems, increased blood pressure, and liver toxicity (when used in large doses).

Prolonged High-Dose Use May Tax Body’s Detox Systems

The findings suggest that prolonged medium- to high-dose usage of acetaminophen could lead to heart issues due to oxidative stress or the accumulation of toxins produced during the breakdown of the medication, potentially overwhelming the body’s detoxification mechanisms.

The observed changes suggest that the hearts of mice treated with acetaminophen had increased stress and mitochondrial dysfunction, Ms. Rivera told The Epoch Times.

The findings highlight the importance of dosage and duration of use; long-term use at medium to high doses may pose greater risks than occasional or low-dose consumption.

The study used a “global proteomic approach,” which enabled the research team to observe the alterations in proteins inside the heart impartially, Ms. Rivera said. “Studies were also conducted on cardiac cells, which complement the proteomic studies,” she added.

A limitation of this experiment is that it was conducted in female mice only, so findings may not apply to the effects of regular acetaminophen usage in male mice or humans.

Acetaminophen Currently Considered Safe: Expert

Acetaminophen is a commonly used drug considered safe at low to moderate dosages of 660 to 1,000 milligrams every four to six hours.

There are no known cardiovascular risks associated with acetaminophen use based on current evidence, Dr. Samantha Lee, director of cardiac telemetry at Staten Island University Hospital, told The Epoch Times.

“A healthy adult can take a lot more acetaminophen than you might expect—up to 4,000 milligrams per day,” she said, though cautioning that an overdose can lead to liver injury.

Daily acetaminophen use could cause rebound headaches, known as medication overuse headaches, treatable by stopping the pain reliever, Dr. Lee noted.

When recommending pain relief for headaches and joint pains, Dr. Lee said she prefers acetaminophen over nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and naproxen, which increase clot formation, blood pressure, and fluid retention, worsening cardiovascular outcomes.

“While this study shows acetaminophen may affect the signaling pathways in the heart of mice models, it does not prove any harmful cardiac side effects in humans,” Dr. Lee said, adding that, like arthritis, cardiac conditions are more common with age, so doctors need pain relief recommendations. “For me, that recommendation is still acetaminophen,” she said.