Acetaminophen is one of the most commonly used medicines in the world. Many people take it to reduce fever, ease headaches, or relieve mild pain such as muscle aches or toothaches.
In pharmacies it is widely available and is often considered safe when used correctly. Most people take acetaminophen in pill or tablet form, swallowing it with water at home.
However, in hospitals doctors sometimes give acetaminophen in a very different way. Instead of taking a pill, patients may receive the drug through an intravenous line, often called an IV.
In this method, the medicine is delivered directly into the bloodstream through a vein. This approach can be very useful for patients who cannot swallow tablets or who need fast and carefully controlled pain relief.
Although IV acetaminophen is widely used in hospitals, researchers have recently discovered a surprising effect that doctors need to be aware of. New scientific studies suggest that when acetaminophen is given through an IV, it can sometimes cause a significant drop in blood pressure.
Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps blood around the body. Maintaining stable blood pressure is important because it ensures that the brain and other organs receive enough oxygen and nutrients.
If blood pressure drops too much, a person may feel dizzy, weak, or faint, and in severe cases it can lead to serious medical problems.
Doctors have long noticed that some patients experience lower blood pressure after receiving IV acetaminophen, especially in intensive care units. Intensive care patients are often very ill and require careful monitoring. But until recently, scientists did not fully understand why this effect occurs.
Research led by Thomas Qvistgaard Jepps and colleagues at the University of Copenhagen helped uncover an explanation. The scientists wanted to understand how IV acetaminophen affects the body differently from the pill form. Their findings provide new clues about how this common drug interacts with blood vessels.
When a person swallows acetaminophen as a tablet, the medicine first travels through the digestive system and then passes through the liver before entering the main bloodstream. The liver processes the drug and changes how it affects the body. This step acts like a filter that modifies the drug before it circulates widely.
In contrast, IV acetaminophen bypasses the digestive system and the liver’s initial processing. Because the medicine enters the bloodstream directly, it reaches blood vessels more quickly and in a different form. This change in the drug’s path through the body appears to influence how blood vessels respond.
The research team discovered that IV acetaminophen interacts with structures in blood vessel cells called potassium channels. These channels are tiny gateways located in the cell membranes of blood vessels. They help control whether blood vessels tighten or relax.
When potassium channels open, they allow potassium ions to move out of the cells. This process causes the muscles in the blood vessel walls to relax. When blood vessels relax and widen, blood can flow more easily through them. As a result, blood pressure decreases.
The scientists found that IV acetaminophen appears to open these potassium channels more than expected. This effect can cause blood vessels to widen suddenly, which may lead to a noticeable drop in blood pressure.
To test their theory, the researchers conducted experiments using laboratory rats. In these experiments they used substances that block the potassium channels.
When the channels were blocked, the sudden drop in blood pressure caused by IV acetaminophen was prevented. This result suggests that potassium channels play a key role in the drug’s effect on blood pressure.
These findings are important for doctors who care for hospitalized patients. Studies show that the blood pressure drop can occur in many patients who receive IV acetaminophen.
In some research, nearly 60 percent of severely ill patients experienced lower blood pressure after receiving the drug through an IV. About one-third of those patients required medical treatment to stabilize their blood pressure.
Understanding this effect is especially important during periods when IV acetaminophen is widely used in hospitals. For example, during the COVID-19 pandemic many patients required intensive care and strong fever or pain control. Knowing how medications behave in these situations helps doctors choose safer treatments.
For people who take acetaminophen as tablets or capsules at home, these findings are not usually a cause for concern. When taken orally, the drug passes through the liver before entering the bloodstream, which changes how it interacts with blood vessels. This pathway greatly reduces the chance of the sudden blood pressure drop seen with IV use.
Still, the research highlights an important lesson in medicine. The way a drug is given—whether swallowed, injected, or delivered through an IV—can greatly change how it behaves in the body and what side effects may occur.
The study led by Jepps and colleagues was published in the scientific journal Atherosclerosis, Thrombosis, and Vascular Biology. The findings provide valuable information for healthcare professionals and may help hospitals improve how they monitor patients receiving IV acetaminophen.
By understanding the biological mechanisms behind this unexpected effect, scientists hope to develop safer treatment strategies. In the future, doctors may be able to prevent sudden blood pressure drops by adjusting dosages or by targeting the potassium channels involved in the process.
Overall, this research shows that even very familiar medicines can still hold surprises. Continued scientific study helps doctors understand these drugs more deeply and ensures that treatments remain as safe and effective as possible for patients.
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 health information, please see recent studies about added sugar in your diet linked to higher blood pressure, and results showing vitamin D could improve blood pressure in people with diabetes.
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