High blood pressure is one of the most common health problems in the world. Many people do not feel sick, but over time it can quietly damage the heart, brain, kidneys, and blood vessels.
Doctors often prescribe medicines called diuretics, sometimes known as “water pills,” to help lower blood pressure. These drugs help the body remove extra salt and water through urine, which lowers pressure inside the blood vessels and protects the heart.
For many years, two diuretics have been widely used: chlorthalidone and hydrochlorothiazide.
Medical guidelines in many countries have suggested that chlorthalidone may be the better first choice because earlier research showed it could control blood pressure well and reduce heart problems. As a result, millions of patients around the world take this medicine every day.
However, a new study from researchers at Columbia University has raised serious questions about whether chlorthalidone is truly the safer option. The scientists examined medical records from more than 730,000 people who were treated for high blood pressure over a period of 17 years.
This large amount of data allowed them to compare the two medicines carefully in real-life patients, not just in small clinical trials.
The researchers found that both medicines worked equally well at preventing major health events such as heart attacks, strokes, and hospital stays for heart failure. This means that, in terms of protecting the heart and blood vessels, neither drug appeared to be better than the other.
The important difference was in the side effects. Patients who took chlorthalidone were much more likely to develop very low potassium levels in their blood.
Potassium is a mineral that the body needs for normal heart rhythm, muscle movement, and nerve signals. When potassium drops too low, it can cause dangerous problems such as irregular heartbeat, muscle weakness, severe fatigue, and even paralysis in extreme cases.
In the study, about 6.3 percent of people taking chlorthalidone developed low potassium, compared with only 1.9 percent of those taking hydrochlorothiazide. Even when doctors used smaller doses of chlorthalidone, the risk was still higher. This finding surprised the researchers because lower doses are usually expected to reduce side effects.
The study also showed that chlorthalidone users had a higher risk of other problems linked to body salt levels. One of these is low sodium, called hyponatremia. Sodium helps control fluid balance and supports brain function.
When sodium becomes too low, people may feel confused, dizzy, or very tired. In severe cases, it can cause seizures or coma. Some patients in the study also showed more signs of kidney trouble while taking chlorthalidone.
These conditions can be especially dangerous because they do not always cause clear symptoms at first. A person may feel normal until the imbalance becomes severe. For this reason, the researchers say patients taking chlorthalidone may need regular blood tests to check mineral levels and kidney function.
This is not the first time scientists have warned about these risks. Earlier studies also suggested that chlorthalidone might cause more problems with body salts than hydrochlorothiazide. Still, many doctors continued to prefer it because of its strong blood pressure effects and long history of use.
The new findings suggest that medical guidelines may need to be reviewed. If two medicines protect the heart equally well, doctors may want to choose the one with fewer risks.
For patients currently taking chlorthalidone, experts say they should not stop their medication suddenly, but they may want to talk with their doctor about whether another option could be safer.
The research was led by George Hripcsak and published in JAMA Internal Medicine. The team hopes their work will encourage doctors to look closely at each patient’s needs instead of relying only on general recommendations. Every person responds differently to medicine, and what is safe for one patient may not be best for another.
This study also reminds us how important it is to keep checking older treatments as new data becomes available. Medicine is always changing as scientists learn more about how drugs affect the body over time. For people living with high blood pressure, choosing the right treatment can have a major impact on long-term health and quality of life.
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