Popular Blood Pressure Medications Linked to Increased Hyponatremia Risk in Older Adults and Women, Study Finds

Popular blood pressure medications, widely used in the UK and beyond, may pose a significant risk to older adults and women, according to a groundbreaking study published in *JAMA Network Open*. The research, conducted in Sweden, highlights a previously underrecognized danger: these drugs could trigger a potentially life-threatening condition called hyponatremia, characterized by dangerously low sodium levels in the blood. This condition, which affects around 1 in 100 people globally, can lead to symptoms ranging from confusion and fatigue to severe seizures in extreme cases. The study's findings have sparked urgent discussions among healthcare professionals about the need to reassess prescribing practices for millions of patients.

The study followed over 159,000 adults who began treatment with either thiazide diuretics—commonly known as "water pills"—or calcium channel blockers. Over several years, researchers tracked the development of hyponatremia in these patients. The results were striking: while younger adults showed minimal risk, older women emerged as the most vulnerable group. Specifically, approximately 3 in 100 women over the age of 80 taking thiazide diuretics developed dangerously low sodium levels. This rate was nearly double that of women on alternative medications, such as calcium channel blockers, where the risk was just over 1 in 100. In contrast, men of the same age group experienced significantly lower risks. The study also noted that the Number Needed to Harm (NNH)—a metric indicating how many patients must take a drug for one to experience harm—was 53 for older women on thiazides, underscoring that this is not an isolated or rare side effect.

Thiazide diuretics, including hydrochlorothiazide, chlorthalidone, and indapamide, are among the most commonly prescribed medications in the UK for managing hypertension and heart failure. These drugs work by promoting the excretion of excess fluid through urine and by dilating blood vessels to lower blood pressure. However, their mechanism of action may also disrupt the body's sodium balance, particularly in older adults whose kidneys and fluid regulation systems are less efficient. The study's authors emphasized that while thiazides remain highly effective for blood pressure control, their potential to cause hyponatremia necessitates careful monitoring.

The implications of these findings are profound, especially given the prevalence of hypertension. Approximately one-third of adults worldwide suffer from high blood pressure, which increases the risk of heart attacks, strokes, kidney disease, and dementia. In the UK alone, over 14.6 million prescriptions for thiazide-like medications were dispensed in 2018. National guidelines, such as those from NICE, still favor thiazides for their cardiovascular benefits, but this study has reignited debates about the need for personalized treatment strategies. Doctors now recommend closer monitoring of sodium levels in older patients, particularly women, who begin thiazide therapy. In some cases, calcium channel blockers may be a safer alternative, as these drugs appear to carry a lower risk of hyponatremia.

Experts stress that the findings should not deter patients from taking necessary medications but instead highlight the importance of proactive management. Regular blood tests, especially during the first few months of treatment, are now advised to detect early signs of sodium imbalance. Patients should also be vigilant for symptoms such as confusion, dizziness, or unexplained fatigue and promptly report these to their general practitioner. For healthcare providers, the study serves as a critical reminder that while thiazides are effective, their use must be tailored to individual risk profiles, particularly for older adults who may be more susceptible to adverse effects.

This research underscores a growing trend in medicine: the shift from one-size-fits-all treatment approaches to more personalized care. As the global population ages, the need to balance the benefits of essential medications with their potential risks becomes increasingly urgent. For now, the study's authors urge clinicians to weigh the pros and cons of thiazide therapy for older patients, ensuring that the pursuit of blood pressure control does not inadvertently compromise other aspects of health.