Study finds notable potassium risk gap between two widely used blood pressure medications

Two commonly prescribed blood pressure drugs may not be as similar in their side effects as many people assume, according to a large observational study.

Researchers found that chlorthalidone was linked to low potassium more often than hydrochlorothiazide.

The distinction is important because both medicines are frequently used to treat hypertension. They are part of a drug class that helps the kidneys eliminate salt and water, which lowers pressure in the blood vessels.

A team at Columbia University reviewed health records from more than 730,000 people across a 17-year span. The study compared the outcomes tied to the two treatments.

Both drugs are well-established blood pressure options. The research was designed to examine whether their safety profiles differ, not to suggest that either medicine does not work.

A key result involved hypokalemia, the medical term for low potassium. Potassium is essential for normal nerve, muscle and heart function, and very low levels can sometimes lead to serious complications.

In the analysis, 6.3 percent of people taking chlorthalidone developed low potassium, compared with 1.9 percent of those taking hydrochlorothiazide. That is a substantial difference in how often the side effect was recorded.

The report also described more electrolyte disturbances and kidney-related problems among chlorthalidone users. The findings underscore that treatment choices involve more than blood pressure numbers alone.

Because the study relied on existing health data, differences between the two patient groups may have influenced the results. An observational study cannot prove that every outcome was directly caused by the drug.

The findings should also not be taken as a reason to stop any prescribed medication. Different drugs can have different benefits and risks depending on a person’s health history and other treatments.

What the research adds is a large-scale comparison of side effects that clinicians can weigh alongside blood pressure control and other evidence. Checking blood chemistry may be especially important when a medication can affect potassium levels.

The results question the idea that closely related blood pressure drugs are automatically interchangeable in every respect. They also show why safety outcomes matter even when medicines are intended to do the same thing.

More research could help clarify how these differences affect long-term health and which patients are most likely to develop complications.

The study highlights the importance of measuring harms as well as benefits. A medication may lower blood pressure effectively while still causing unwanted changes in lab values, and large datasets can uncover uncommon outcomes that smaller studies may miss.

If you are interested in this topic, please read articles about What should know about high blood pressure drugs and their side effects, and Potassium may be key to lowering blood pressure, study finds.

For more information, please see articles about Why potassium matters for your blood pressure health, and Sodium intake and high blood pressure: What to know.

Source: Columbia University.