Acetaminophen, also known as paracetamol in many countries, is one of the most widely used pain relievers in the world.
Millions of people take it every day for headaches, fever, muscle pain, arthritis, and common illnesses such as colds or the flu.
When used correctly, it is generally considered safe and effective.
Most people take acetaminophen by mouth in the form of tablets, capsules, or liquid medicine. However, in hospitals, doctors often give the drug through an intravenous line, also called an IV. This allows the medicine to go directly into the bloodstream through a vein.
IV acetaminophen is especially useful for patients who are unable to swallow, are unconscious, recovering from surgery, or are critically ill. It also works faster than pills because it reaches the bloodstream immediately. Doctors can carefully control the exact amount given, which is important in emergency and intensive care situations.
But doctors have noticed a troubling problem for years. Some patients who receive IV acetaminophen suddenly experience a large drop in blood pressure. In severe cases, this can become dangerous and may require urgent medical treatment.
Now, researchers from the University of Copenhagen believe they have uncovered why this happens.
The scientists found that around six out of ten critically ill patients experience some degree of blood pressure drop after receiving IV acetaminophen. For roughly one-third of these patients, the drop becomes serious enough that doctors must step in to stabilize their blood pressure.
Low blood pressure can be especially dangerous for patients already fighting severe illness, infection, or organ problems. If blood pressure falls too low, the body may struggle to deliver enough oxygen to important organs such as the brain, heart, and kidneys.
Despite this side effect, IV acetaminophen remains widely used because it still offers many important benefits and is usually safe when used carefully.
To understand why this reaction happens, the researchers examined how the body processes acetaminophen differently depending on how it enters the body.
When people swallow acetaminophen, the medicine first passes through the liver before reaching the bloodstream. The liver helps break down the drug in a controlled way. However, when acetaminophen is given through an IV, it bypasses the liver at first and spreads quickly throughout the body.
Because of this difference, the body produces different leftover chemicals, known as byproducts, during the breakdown process. The researchers discovered that some of these byproducts appear to affect special structures called potassium channels.
Potassium channels help control how blood vessels tighten and relax. Blood vessels constantly adjust their size to help regulate blood pressure. If blood vessels relax too much, blood pressure can suddenly fall.
The study found that the byproducts created after IV acetaminophen may overstimulate these potassium channels, causing blood vessels to widen more than normal. This excessive relaxation appears to trigger the rapid blood pressure drop seen in some hospital patients.
To test their theory, the researchers carried out experiments in rats. They used another drug designed to block certain potassium channels before giving IV acetaminophen. The results were striking. The rats experienced much smaller drops in blood pressure when the potassium channels were blocked.
This suggests that targeting these channels could someday help doctors prevent or reduce this dangerous side effect in patients receiving IV acetaminophen.
The researchers emphasized that this problem mainly affects IV acetaminophen rather than the standard tablets people take at home. For most healthy people using acetaminophen by mouth at recommended doses, the medicine remains very safe.
Doctors are not advising people to stop taking acetaminophen for everyday pain relief or fever control. Instead, the findings are mainly important for hospital settings where IV versions are commonly used in very sick patients.
The research has become even more relevant since the COVID-19 pandemic increased the use of IV acetaminophen in hospitals worldwide. Many hospitalized COVID-19 patients received IV acetaminophen to control fever and pain, making it especially important for doctors to understand possible side effects.
Scientists hope these findings may eventually lead to safer treatment strategies for critically ill patients. By better understanding how the drug affects blood vessels and blood pressure, doctors may be able to reduce complications while still benefiting from the pain-relieving effects of acetaminophen.
Researchers are also continuing to study many other factors related to blood pressure and heart health. Some studies suggest that olive oil may help support healthier blood pressure levels. Scientists are also exploring whether certain B vitamins could help people with difficult-to-control high blood pressure.
If you care about high blood pressure, please read studies that early time-restricted eating could help improve blood pressure, and natural coconut sugar could help reduce blood pressure and artery stiffness.
For more information about blood pressure, please see recent studies about How to eat your way to healthy blood pressure and results showing that Modified traditional Chinese cuisine can lower blood pressure.
