High blood pressure is extremely common and often causes no obvious symptoms.
Over time, however, the extra pressure can damage blood vessels and increase the risk of heart attack, stroke, heart failure and kidney disease.
Medicines are often needed when lifestyle changes are not enough to bring blood pressure into a healthy range.
Researchers at Columbia University examined the safety of two widely used medicines for high blood pressure: chlorthalidone and hydrochlorothiazide. Both belong to a group of medicines called diuretics, sometimes known as water pills. They help the kidneys remove extra salt and water from the body, which can lower blood pressure.
Chlorthalidone has often been favored by some doctors because it remains active in the body for longer and has been supported by earlier cardiovascular research.
Hydrochlorothiazide, however, is also widely prescribed. The researchers wanted to know whether chlorthalidone actually produced better heart outcomes and whether the two medicines differed in safety.
The team analyzed medical information from more than 730,000 people treated for high blood pressure. The data came from several large databases and covered many years of real-world treatment. This allowed the researchers to compare outcomes in a much larger population than would normally be possible in a single clinical trial.
They found no clear cardiovascular advantage for chlorthalidone. People taking the two drugs had similar rates of major problems such as heart attacks, heart failure and strokes. But important differences appeared when the researchers looked at side effects.
Low potassium was much more common among people taking chlorthalidone. About 6.3% of chlorthalidone users developed low potassium levels, compared with about 1.9% of people taking hydrochlorothiazide. Overall, chlorthalidone was associated with roughly three times the risk of this problem.
Potassium is an essential mineral that helps nerves send signals and allows muscles to work normally. It is particularly important for the heart because abnormal potassium levels can interfere with its electrical activity. Very low potassium can cause weakness, muscle cramps, tiredness and, in serious cases, dangerous changes in heart rhythm.
The study also linked chlorthalidone with higher rates of several other problems involving the kidneys and the body’s balance of minerals and salts. These included changes in sodium and other electrolytes.
Because the kidneys play a major role in controlling these substances, kidney function and electrolyte levels are often monitored in people taking diuretics.
The results do not mean chlorthalidone is an unsafe medicine or that everyone taking it should switch drugs.
Many people use it successfully, and the best blood pressure treatment depends on a person’s health, other medicines and individual risks. Patients should not stop or change a prescribed blood pressure medicine without speaking with their healthcare provider.
Instead, the research suggests that doctors may need to consider the safety differences when choosing between these two medicines.
People who are more likely to develop kidney problems or abnormal potassium levels may need particularly careful monitoring. Simple blood tests can help doctors detect electrolyte changes before they become serious.
Medication is only one part of controlling hypertension. Regular exercise, eating plenty of fruits and vegetables, reducing excess salt, maintaining a healthy weight, avoiding smoking and limiting alcohol can all support healthier blood pressure. For many people, these habits work alongside medication rather than replacing it.
The Columbia University-led research was published in JAMA Internal Medicine. The findings challenge the idea that chlorthalidone should automatically be preferred over hydrochlorothiazide and highlight why both the benefits and possible side effects of blood pressure medicines need to be considered.
If you care about blood pressure, please read studies about unhealthy habits that could increase high blood pressure risk, and people with severe high blood pressure should reduce coffee intake.
For more information about blood pressure, please see recent studies that early time-restricted eating could help improve blood pressure, and results showing plant-based foods could benefit people with high blood pressure.
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