Climate Change-Induced Extreme Heat Events and Chronic Disease Exacerbation: A Review of Primary Care Risk Stratification and Patient Management

In 2024, the annual global surface temperature rose more than 1.5 °C above pre-industrial levels for the first time. This single-year figure is not the same as the long-term warming limit set by the Paris Agreement, but it signals a rising heat-related risk. Extreme heat is already the deadliest weather hazard in the United States, yet most outpatient clinics have no structured protocol for vulnerable patients. This narrative review does three things: it explains how heat stress injures compromised cardiovascular and renal systems, catalogs the primary care medications that impair thermoregulation, and offers a Heat Action Plan (HAP) toolkit for family medicine clinics. We searched PubMed, EMBASE, Google Scholar, and Web of Science for work published from 2000 to May 2026, supplemented by WHO, CDC, and national heat-health guidelines. Patients with cardiovascular disease, chronic kidney disease, diabetes, obesity, and serious mental illness face disproportionate risk during heat events. More than 20 drug classes, among them diuretics, beta-blockers, anticholinergics, and renin–angiotensin–aldosterone system inhibitors, weaken heat defense by blunting sweating, reducing cardiac output, or suppressing thirst. We present a three-tier risk classification and a four-stage toolkit that, when built into routine chronic disease care, may help reduce preventable heat-related illness and death.