The body reacts differently to medications in hot weather, study reveals

Ambient temperature has a decisive influence on the action of certain medications. Consider an example: a doctor prescribes 50 mg of a beta-blocker twice a day for a 70-year-old man with chronic heart failure and arrhythmias. Under normal conditions, this treatment is sufficient. But what happens when the outside temperature reaches 40 degrees?

To maintain a stable internal temperature, the body responds to extreme heat by increasing sweating, dilating blood vessels, and increasing blood flow to the skin. If these regulatory mechanisms fail, disorders such as dizziness, headaches, cramps, circulatory problems, arrhythmias, heart attacks, or even heat stroke occur.

In these circumstances, those taking medication should hydrate more than usual, as dehydration potentiates the effects of the drugs and can dangerously intensify their side effects. This is particularly true for beta-blockers, explains Julia Stingl, medical director of the Department of Clinical Pharmacology at Heidelberg University Hospital. In fact, the so-called Heidelberg Heat Table has become a reference guide for adjusting dosages during heat waves.

The problem isn't limited to beta-blockers: diuretics and laxatives (which promote fluid loss), psychotropic drugs and antidepressants, anticholinergics, antihistamines, and even common painkillers like aspirin or ibuprofen are also affected. To avoid overdose, doses should be adjusted—usually reduced—on an individual basis during periods of intense heat. However, many people are unaware of this, among other reasons because package inserts rarely include warnings on the subject.

According to the World Health Organization (WHO), approximately 490,000 people die each year worldwide due to high temperatures, a figure that has been increasing in recent decades. Part of this mortality, Stingl warns in an interview with DW, is related to changes in the effectiveness of medications and the intensification of their adverse effects in extreme heat conditions.

“We see this clearly in clinical practice,” he says. “Climate change is increasing mortality, especially in older people on multiple medications. The most intense side effects cause dizziness, loss of balance, coordination problems, and even confusion. This translates into more falls and more emergency room admissions during hot summers.”

So-called direct heat-related deaths are usually counted only when the diagnosis is heat stroke or acute organ failure on extremely hot days. But broader estimates, such as those by the WHO, also include excess mortality in heat waves: heart attacks, strokes, and other events associated with rising temperatures, considered indirect heat-related deaths.

In Europe, more than 47,000 people died from this cause in 2023, according to a study led by the Barcelona Institute for Global Health based on Eurostat data . In recent years, the figures have ranged between 30,000 and 70,000 deaths, depending on the severity of the heat waves. The hardest-hit countries were Greece, Bulgaria, Italy, and Spain. In Germany alone, between 2,800 and 3,000 heat-related deaths were recorded in 2024.