Two widely used blood pressure medicines can both lower blood pressure, but one may cause more side effects than the other.
A large study led by researchers at Columbia University compared chlorthalidone with hydrochlorothiazide in more than 730,000 people treated for high blood pressure.
The researchers examined health records collected over 17 years, making the study one of the largest comparisons of these two medicines. The research was led by Dr. George Hripcsak and published in JAMA Internal Medicine.
High blood pressure, also called hypertension, is extremely common and often causes no obvious symptoms. Over time, however, the extra pressure can damage blood vessels and raise the risk of heart attack, stroke, heart failure, kidney disease, and other serious health problems.
Doctors may recommend lifestyle changes and medication to bring blood pressure down. Among the medicines commonly prescribed are diuretics, sometimes called “water pills,” which help the kidneys remove extra salt and water from the body.
Chlorthalidone and hydrochlorothiazide are both diuretics and have been used for decades. Because they work in similar ways, researchers wanted to know whether one offered a better balance between effectiveness and safety.
The study found no clear cardiovascular advantage for chlorthalidone compared with hydrochlorothiazide. However, chlorthalidone was linked to a higher risk of several unwanted effects, particularly problems involving potassium and the kidneys.
Potassium is an important mineral that helps nerves, muscles, and the heart work normally. When potassium in the blood falls too low, a condition known as hypokalemia can develop.
Low potassium can cause weakness, tiredness, muscle cramps, and abnormal heart rhythms. Severe cases can become dangerous, especially for people who already have heart or kidney problems.
In the study, people taking chlorthalidone were almost three times as likely to develop low potassium as those taking hydrochlorothiazide. Hypokalemia occurred in about 6.3% of people taking chlorthalidone, compared with about 1.9% of those taking hydrochlorothiazide.
Chlorthalidone was also associated with higher rates of some kidney problems and other changes in the balance of minerals and salts in the blood. These differences were important because both medicines are widely prescribed to people who may take them for many years.
The findings add to a long-running discussion about which diuretic should be preferred for treating high blood pressure. Chlorthalidone has sometimes been favored because it stays active in the body longer and has been considered especially effective at controlling blood pressure.
The researchers said the safety findings should be considered when doctors choose between the two medicines. However, the results do not mean that everyone taking chlorthalidone should stop using it, because the best treatment depends on a person’s medical history, blood pressure, other medicines, and individual risks.
Medication is also only one part of controlling high blood pressure. Eating less salt, staying physically active, maintaining a healthy weight, avoiding smoking, limiting alcohol, and following medical advice can all help protect the heart and blood vessels.
Regular blood pressure checks are important because hypertension can remain unnoticed for years. Doctors may also use blood tests to monitor potassium levels and kidney function when people take certain blood pressure medicines.
For people already taking chlorthalidone or hydrochlorothiazide, the study provides useful information rather than a reason to change treatment on their own. Anyone concerned about side effects or whether their medicine is still the best choice should discuss the findings with their doctor before making changes.
Copyright © 2026 Knowridge Science Report. All rights reserved.
