A large study has found an important safety difference between two common medicines used to treat high blood pressure.
Both chlorthalidone and hydrochlorothiazide can lower blood pressure, but chlorthalidone was linked to more problems with potassium, other body salts, and kidney function.
The research was led by Dr. George Hripcsak and colleagues at Columbia University and was published in JAMA Internal Medicine. The researchers examined health information from more than 730,000 people treated for high blood pressure and compared the outcomes of patients taking the two medicines.
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 called diuretics are often used to bring blood pressure down. They help the kidneys remove extra salt and water from the body, which reduces the amount of fluid moving through blood vessels.
Chlorthalidone and hydrochlorothiazide belong to this general group and have been prescribed for many years. Some treatment guidelines and experts have favored chlorthalidone because it stays active in the body longer and earlier research suggested it might offer strong protection against heart problems.
The Columbia study, however, found no clear advantage for chlorthalidone in preventing major heart-related outcomes compared with hydrochlorothiazide. Both medicines were similarly effective when researchers looked at problems such as heart attack, stroke, and heart failure.
The biggest difference involved side effects. About 6.3% of patients taking chlorthalidone developed low potassium levels, 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, muscle cramps, tiredness, or abnormal heart rhythms, although mild cases may cause few noticeable symptoms.
Chlorthalidone was also associated with a greater risk of several other problems involving the body’s balance of minerals and salts. Researchers additionally found signs of a higher risk of some kidney complications among people taking the drug.
These findings do not mean that chlorthalidone is unsafe for everyone or that patients should stop taking it. A medicine that works well for one person may not be the best choice for another, and suddenly changing blood pressure treatment without medical advice can itself create risks.
Instead, the study suggests doctors should consider both benefits and possible side effects when choosing between the two drugs. People taking chlorthalidone may also need blood tests to make sure their potassium, other important minerals, and kidney function remain at healthy levels.
Medication is only one part of controlling high blood pressure. Regular physical activity, eating a balanced diet, limiting excess salt, avoiding smoking, maintaining a healthy weight, and limiting alcohol can all help support healthier blood pressure.
Checking blood pressure at home can also give doctors useful information about how well treatment is working. Because blood pressure can change throughout the day, repeated readings often provide a better picture than a single measurement.
The study adds useful evidence to a long-running discussion about which of these two widely used medicines should be preferred. It suggests that stronger or longer-lasting blood pressure lowering does not automatically make a drug the best option if it also produces more unwanted effects.
For patients, the main message is not to choose or change a medicine based on one study alone. The best treatment depends on a person’s blood pressure, kidney health, other medical conditions, other medicines, and risk of side effects, making an individual discussion with a doctor important.
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