Millions of people around the world live with high blood pressure, also called hypertension.
Many people do not notice any symptoms, but high blood pressure can quietly damage the heart, brain, kidneys, and blood vessels over many years.
If it is not treated, it greatly increases the risk of heart attack, stroke, heart failure, kidney disease, and other serious health problems. Because of this, doctors often recommend healthy lifestyle changes together with medicines to help lower blood pressure and protect long-term health.
Among the medicines used for high blood pressure are two well-known drugs called chlorthalidone and hydrochlorothiazide.
These medicines belong to the same family of drugs and help the body remove extra salt and water through urine.
This lowers the amount of fluid in the blood vessels, making it easier for blood to flow and helping reduce blood pressure. Doctors have prescribed both medicines for many years, and both have been considered effective choices.
Now, a very large study from Columbia University has provided new information that may help doctors choose between these two medicines more carefully.
The research followed more than 730,000 patients over a period of 17 years, making it one of the biggest studies ever carried out on these medications. Instead of only looking at how well the drugs lowered blood pressure, the researchers also examined how safe they were during everyday use.
The study found that both medicines were able to control high blood pressure, but they did not have the same safety profile. People who took chlorthalidone had a much greater chance of developing several important side effects than people who took hydrochlorothiazide.
The biggest concern was a condition called hypokalemia, which means the level of potassium in the blood becomes too low.
Potassium is a mineral that the body needs every day. It helps the heart beat normally, allows muscles to work properly, and supports healthy nerve signals.
When potassium levels become too low, people may feel weak, tired, or confused. In more serious cases, low potassium can cause dangerous changes in heart rhythm. It may also increase the risk of kidney problems and type 2 diabetes in some people.
The difference between the two medicines was clear. About 6.3 percent of people taking chlorthalidone developed low potassium levels, while only 1.9 percent of those taking hydrochlorothiazide had the same problem.
The researchers also found that this higher risk remained even when chlorthalidone was given in smaller doses.
The study showed other safety concerns as well. People taking chlorthalidone were more likely to develop problems with the balance of important minerals in the body, known as electrolytes.
These minerals help control many body functions, including muscle movement, nerve activity, and the amount of water inside the body. Chlorthalidone users also had a higher chance of developing kidney problems, which can become serious if they are not found and treated early.
These findings have led many experts to think more carefully about current treatment recommendations. Chlorthalidone has often been recommended because it lowers blood pressure well, but this new evidence suggests that doctors should also pay close attention to its possible risks.
If a patient is prescribed chlorthalidone, regular blood tests to check potassium levels and kidney function may help find problems before they become serious.
The results also remind us that there is no single blood pressure medicine that is best for everyone. Every patient is different. Age, other health conditions, kidney function, other medicines, and the risk of side effects should all be considered before choosing treatment. A medicine that works well for one person may not be the best choice for someone else.
Medicine is only one part of controlling high blood pressure. Eating less salt, choosing healthy foods, staying physically active, maintaining a healthy weight, avoiding smoking, limiting alcohol, getting enough sleep, and managing stress can all help lower blood pressure.
Many doctors also encourage people to check their blood pressure at home and attend regular medical appointments so treatment can be adjusted when needed.
The researchers say that large, long-term studies like this are valuable because they can reveal problems that may not appear in smaller clinical trials. Information collected from hundreds of thousands of patients over many years gives doctors a clearer picture of how medicines perform in everyday life.
The study was led by Dr. George Hripcsak of Columbia University and was published in the journal JAMA Internal Medicine. The findings provide important evidence that can help doctors and patients make better-informed decisions when choosing blood pressure treatment.
While both chlorthalidone and hydrochlorothiazide remain effective medicines for lowering blood pressure, the research suggests that hydrochlorothiazide may have fewer serious side effects for many patients. The study also highlights the importance of regular monitoring, careful treatment decisions, and a personalized approach to protecting heart health.
If you care about high blood pressure, please read studies about what to eat and to avoid for high blood pressure, and 12 foods that lower blood pressure.
For more health information, please see recent studies about the connection between potato and high blood pressure, and how to eat your way to healthy blood pressure.
