Psychotropic medication safety during extreme heat

People receiving psychiatric treatment can experience substantial harm during extreme heat, but evidence that identifies vulnerable patients does not necessarily establish the benefit of changing their medication. This critical narrative review examines human experimental, pharmacoepidemiological, pharmacokinetic, and implementation evidence, with emphasis on antipsychotics, antidepressants, and lithium. Targeted searches of PubMed and Europe PMC were supplemented by OpenAlex discovery searches, reference checking, and official guidance. Studies of heatwave mortality associate antipsychotic exposure with increased odds of death, including an adjusted odds ratio of 2.43 (95% CI 1.52-4.01) among people with schizophrenia during the 2021 British Columbia heat event. However, a Japanese self-controlled study found similar heatwave-associated increases in heat illness during periods with and without antipsychotic prescriptions. Controlled physiology studies predominantly involve small samples of healthy men and brief exposures, limiting their application to prolonged heat in psychiatric populations. Lithium studies further illustrate that plausible dehydration-related toxicity does not imply a clinically important average seasonal increase in drug concentration. These findings address different causal questions and should not be treated as interchangeable estimates of medication harm. A clinically useful synthesis separates baseline vulnerability, medication-associated risk, modification of heat effects, and the benefits and harms of a specific prescribing strategy. Current evidence supports individualized heat planning, access to cooling, and medication review, but does not establish the net benefit of routine heat-triggered psychotropic discontinuation. Comparative studies should measure psychiatric destabilization alongside heat illness and evaluate practical protection strategies under real-world exposure conditions.