“Take once daily” assumes a lot in just three words. Prescription labels tell us when to take a medication, whether to take it with food, and what substances to avoid, but rarely anything about the temperature outside. That omission looked less trivial during British Columbia’s 2021 heat dome, when hundreds of people died from heat-related causes. Boudreault et al. (2025) compared 504 heat-related community deaths with 2,520 matched controls and found that recent dispensations of anti-Parkinson drugs, antiepileptics, and psycholeptics were associated with higher odds of heat-related death, even after adjustment for chronic disease (Figure 1). Association is not causation, but it raises an uncomfortable question: how much does a prescription assume about the environment in which it is taken?
The biology gives that association a plausible mechanism. To keep core temperature stable, the body increases skin blood flow and sweating, two heat-loss pathways that medications can disrupt (Wee et al. 2023). Across 35 randomized heat-stress studies, atropine, an anticholinergic medication, raised core temperature by an average of 0.42°C at air temperatures of at least 30°C while reducing sweating; non-selective beta-blockers, medications that can also interfere with the body’s heat-loss responses, raised it by 0.11°C (Hospers et al. 2024). Even relatively small increases in core temperature can become more concerning during heat stress, when the body is already working to dissipate excess heat.
But medication–heat interactions are not just a thermostat problem. Heat-related illness can involve fluid and electrolyte imbalance. Risk can be compounded by age, multimorbidity (having multiple chronic conditions), and polypharmacy (taking multiple medications at once) (Tews et al. 2026). Nor is the relationship one-way. Elevated temperature can increase delivery of some transdermal and topical drugs by changing drug release, skin permeability, blood flow, and dermal clearance (Hao et al. 2016). Heat can therefore alter both drug action and, for some formulations, drug delivery.
The stranger part is how thin the evidence becomes when we ask who was actually studied. Hospers et al. (2024) found only 353 participants across those 35 studies: 337 men and just 16 women. With women making up less than 5% of participants, it is difficult to know how well these findings generalize across sexes. The average participant was under 30, and only one study included a clinical population. A 2026 review of 61 primary studies similarly found limited evidence-based guidance for managing medication–heat interactions in older adults (Tews et al. 2026). The populations most relevant to these risks, including older adults, people with chronic illness, and those taking multiple medications, remain poorly represented in controlled evidence.
Those blind spots would matter in a stable climate. We do not have one. Across 732 locations in 43 countries, 37% of warm-season heat-related deaths between 1991 and 2018 were attributable to human-induced climate change (Vicedo-Cabrera et al. 2021). Climate change is often framed as a future pressure on healthcare, but it may also be rewriting the assumptions underneath treatments we already use.
A prescription is not an isolated chemical instruction. It is an interaction between a drug, a body, and an environment. If one of those three is changing, medicine cannot keep treating it as background.
References
Boudreault, Jeremie, Kathleen E. McLean, and Sarah B. Henderson. 2025. “Exploring the Relationship between Medications and Heat-Related Community Deaths during the 2021 Heat Dome: A Hybrid Approach Using Machine Learning.” eBioMedicine 117: 105788. https://doi.org/10.1016/j.ebiom.2025.105788.
Hao, Jinsong, Priyanka Ghosh, S. Kevin Li, Bryan Newman, Gerald B. Kasting, and Sam G. Raney. 2016. “Heat Effects on Drug Delivery across Human Skin.” Expert Opinion on Drug Delivery 13 (5): 755–768. https://doi.org/10.1517/17425247.2016.1136286.
Hospers, Lily, Gabrielle A. Dillon, Andrew J. McLachlan, et al. 2024. “The Effect of Prescription and Over-the-Counter Medications on Core Temperature in Adults during Heat Stress: A Systematic Review and Meta-Analysis.” EClinicalMedicine 77: 102886. https://doi.org/10.1016/j.eclinm.2024.102886
Tews, Lily M., Daniel T. Abazia, Hayley Blackburn, Kiri Carmody, and Mary Barna Bridgeman. 2026. “Recognizing and Mitigating the Effects of Medication on Heat-Related Illness in Older Adults: A Scoping Review.” Pharmacy 14 (3): 74. https://doi.org/10.3390/pharmacy14030074.
Vicedo-Cabrera, A. M., N. Scovronick, F. Sera, et al. 2021. “The Burden of Heat-Related Mortality Attributable to Recent Human-Induced Climate Change.” Nature Climate Change 11 (6): 492–500. https://doi.org/10.1038/s41558-021-01058-x
Wee, Jericho, Xiang Ren Tan, Samuel H. Gunther, et al. 2023. “Effects of Medications on Heat Loss Capacity in Chronic Disease Patients: Health Implications Amidst Global Warming.” Pharmacological Reviews 75 (6): 1140–1166. https://doi.org/10.1124/pharmrev.122.000782
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