New research has revealed that a common medication might not be safe for everyone.

Acetaminophen, brand name Tylenol, is a pain reliever and fever reducer that's often included in other drugs, such as cold and flu medicines.

The U.K.-based study — published in Arthritis Care & Research, an official journal of the American College of Rheumatology — analyzed the safety of the drug in older individuals.

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The researchers looked at data for more than 180,000 acetaminophen users compared to 400,000 non-users from 1998 to 2018.

The findings revealed that the use of acetaminophen – sometimes also called paracetamol – was associated with an increased risk of serious medical complications.

This includes peptic ulcer bleeding, uncomplicated peptic-ulcers, lower gastrointestinal bleeding, heart failure, hypertension and chronic kidney disease.

In a University of Nottingham press release sent to Fox News Digital, lead study author Professor Weiya Zhang, PhD, clarified that long-term use of the drug should be "carefully considered."

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"Due to its perceived safety, paracetamol has long been recommended as the first-line drug treatment for osteoarthritis by many treatment guidelines, especially in older people who are at higher risk of drug-related complications," he wrote.

"While further research is now needed to confirm our findings, given its minimal pain-relief effect, the use of paracetamol as a first-line painkiller for long-term conditions such as osteoarthritis in older people needs to be carefully considered."

Dr. Marc Siegel, clinical professor of medicine at NYU Langone Health and senior medical analyst at Fox News, shared his reaction with Fox News Digital.

"It is generally accepted doctrine that acetaminophen is not associated with GI bleeding or advancing kidney disease, but the thinking is starting to change on this front," said the doctor, who was not involved in the study.

There is evidence suggesting that acetaminophen "modulates the same cyclooxygenase-related pathways" as anti-inflammatory drugs like ibuprofen, which can "increase adverse GI side effects," according to Siegel.

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The large U.K. study, the doctor commented, is limited by "being observational," as well as by an "inability to track over-the-counter as opposed to prescriptions, which were tracked."

Another potential limitation was that some users had other contributing factors and behaviors, such as smoking and obesity.

"Still, this is a good reminder that all medicines used chronically have side effects, and we are not always sure what they are," he said. "This is why we continue to do post-market analysis and to re-evaluate medicines."

He continued, "And yes, over-the-counter medications are still medications. Acetaminophen is well-known for its liver toxicity, but there are other side effects as well, as this study suggests."

Fox News Digital reached out to Kenvue, Inc., maker of Tylenol, requesting comment on the study. 

Risks for older adults

Gerontologist Dr. Macie P. Smith in South Carolina, who was not involved in the study, also reacted to the findings.

"I am happy someone is talking about the side effects of certain medications and how they disproportionately impact … those over [age] 65," she told Fox News Digital.

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Several medications are not recommended for the older adult population, Smith said.

"Simply because they could tolerate the medications at a younger age does not mean their body can tolerate the same medications at an older age, since their body and brain will change as they age," she noted.

Some of the complications mentioned in the study, such as GI bleeding, hypertension and kidney disease, can increase the risk of stroke, Alzheimer’s disease, dementia, even premature death, according to Smith.

"I would recommend that older adults consult with their primary care doctor before taking any over-the-counter medications, since acetaminophen can be found in cold and flu medications and in creams and [ointments]," she advised.

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"Anything that is identified as a medication or drug should be discussed with the doctor, as geriatrics is a specialized practice and those who fall under this category should receive specialized care."

Smith also recommended that older adults use only one pharmacy, so the pharmacist can consult the patient's "running ledger" of prescription medications.

"If someone over the age of 65 comes in for over-the-counter medications, the pharmacist can easily and quickly check for medication side effects and possible interactions between their prescription and OTC medications," she said.

Acetaminophen in particular should be "taken with caution" and under the direction of a doctor for those 65 and older, she cautioned.

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Smith urged older individuals and their caretakers to "read the important information that comes with any and all medications."

She added, "Don’t hesitate to speak to the pharmacist and/or your doctor about the risks and the benefits, then make an informed decision and choose well."

Fox News Digital reached out to a number of drug manufacturers for comment.