A widely used medicine for high blood pressure may cause more unwanted effects than a similar drug, according to a large study led by researchers at Columbia University.
The findings raise questions about whether chlorthalidone should always be preferred over hydrochlorothiazide, another common blood pressure medicine.
High blood pressure, or hypertension, means blood is pushing against artery walls with too much force over time. It often causes no obvious symptoms, but it can slowly damage blood vessels and increase the risk of heart disease, stroke and kidney problems.
Medicines called diuretics are often used to lower blood pressure. They help the kidneys remove extra salt and water from the body, reducing the amount of fluid moving through the blood vessels.
Chlorthalidone and hydrochlorothiazide are two commonly used medicines in this group. Chlorthalidone has sometimes been preferred because it lasts longer in the body and has been thought to offer stronger protection against heart problems.
To compare the two medicines, researchers examined 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 medical care.
The researchers found no clear evidence that chlorthalidone was better at preventing heart attacks, heart failure or strokes than hydrochlorothiazide. However, important differences appeared when the team looked at side effects.
People taking chlorthalidone were almost three times as likely to develop dangerously low potassium levels. About 6.3% of chlorthalidone users developed low potassium, compared with about 1.9% of people taking hydrochlorothiazide.
Potassium is an important mineral that helps nerves, muscles and the heart work normally. When potassium becomes too low, people may experience weakness, tiredness, muscle cramps or abnormal heart rhythms, although mild cases may cause few noticeable symptoms.
Kidney problems were another concern. The study linked chlorthalidone with higher rates of sudden kidney injury and long-term kidney disease, as well as several other changes in the balance of minerals and salts in the blood.
These findings do not mean chlorthalidone is unsafe for everyone. The medicine can effectively lower blood pressure, and doctors may still decide that it is the right choice for some patients based on their overall health and individual risks.
The results do suggest that people taking chlorthalidone may need appropriate monitoring, particularly of potassium levels and kidney function. Patients should not stop or change a blood pressure medicine on their own, because uncontrolled high blood pressure can itself cause serious harm.
Lifestyle changes can also play an important role in controlling blood pressure. Eating more fruits, vegetables and whole grains, limiting excess salt, exercising regularly, maintaining a healthy weight, avoiding smoking and limiting alcohol can all support better heart and blood vessel health.
The research was published in JAMA Internal Medicine in 2020. Led by George Hripcsak and colleagues at Columbia University Irving Medical Center, the study used a large international collection of health records to compare the safety and effectiveness of the two drugs.
Because the research was based mainly on existing health records rather than a trial that randomly assigned people to each medicine, it cannot prove that chlorthalidone directly caused every additional problem. Still, the large number of patients gives doctors useful information when choosing between two widely prescribed treatments.
For people already taking chlorthalidone, the findings are a reason for awareness rather than alarm. Regular medical checkups and blood tests can help doctors identify changes in potassium or kidney function and decide whether treatment needs to be adjusted.
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.
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