Medicines that can raise your risk in a heat wave, and what to ask your doctor

The short answer

Yes, some common medicines can make heat more dangerous. The Centers for Disease Control and Prevention (CDC) names, among others, water pills (diuretics), several blood pressure and heart medicines, lithium, antipsychotics, some antidepressants, ADHD stimulants and some nonprescription sleep and allergy medicines. Depending on the medicine, it can dull thirst, change sweating, lower blood pressure, drain fluid and salts, or build up in the blood when you are low on fluids.

• Do not stop or change a medicine on your own. CDC asks clinicians to remind patients not to stop medicines suddenly without a plan.
• Ask before the heat arrives. Take your full medicine list, including nonprescription products and supplements, to your clinician or pharmacist and ask for a written hot-day plan.
• Protect the medicines, too. Heat can weaken insulin, make an epinephrine auto-injector (such as an EpiPen) less reliable and burst an inhaler canister. Do not leave medicines in a parked car.

How medicines change the way your body handles heat

Your body cools itself by sweating, by sending more blood to the skin so heat can escape, and by making you thirsty so you replace lost fluid. CDC describes medicines interfering in several ways:

• Thirst and fluids: less thirst, fluid loss, and low blood pressure that can cause fainting and falls.
• Cooling: less sweating (or more, which drains fluid), less blood flow to the skin, or weaker temperature control by the brain.
• Blood chemistry: imbalance of salts and minerals (electrolytes), or buildup of medicines with a narrow safe range, such as lithium and carbamazepine, when you are low on fluids.
• Alertness: sleepiness or slower thinking (for example, from opioids or benzodiazepines), which makes falls more likely and can dull thirst.

Medicine groups that CDC flags

This table summarizes CDC's guidance for clinicians, first published in 2024 and last reviewed September 18, 2025. CDC says its list "is not comprehensive." A medicine missing here may still matter, so ask about every medicine you take.

The examples come from CDC, except ibuprofen and naproxen, added as familiar NSAIDs. CDC also mentions laxatives (fluid and salt loss), alcohol (more sweating and urination, and less ability to sense heat), and cocaine and MDMA (less sweating and a blunted sense of heat). Over-the-counter medicines count, too.

Children, older adults and sun-sensitive skin

Children and teens. CDC lists older, drowsy-type antihistamines such as diphenhydramine, ADHD stimulants such as methylphenidate, tricyclic antidepressants, SSRIs and diuretics as medicines that may raise a young person's risk of heat illness. If your child takes one of these and plays sports or spends long days outside, ask the prescriber or pharmacist what to watch for.

Older adults. CDC stresses a medicine review for people who take several medicines whose effects can add up, especially older adults. Bring every bottle, or a complete list that includes vitamins, supplements and nonprescription products. Managing Multiple Medications Safely explains how to keep one accurate list.

Sun-sensitizing medicines. Some antibiotics (metronidazole, tetracyclines and fluoroquinolones) and antifungals (flucytosine, griseofulvin and voriconazole) can cause a sunburn-like rash. CDC advises limiting sun, wearing protective clothing and using broad-spectrum sunscreen with SPF 30 or higher.

Don't stop your medicine: get a hot-day plan instead

A blood pressure pill, mood stabilizer or seizure medicine may be what keeps a serious condition under control. CDC tells clinicians to remind patients "to avoid abruptly stopping any medications without having a plan in place." CDC also describes what a plan can cover, so you can ask for each part:

• Your list. Which of my medicines interact with heat, and do any add to each other's effects?
• Dose or timing. Should anything change on hot days? CDC says this is decided person by person; only your prescriber can make a change.
• Fluid limits. If you have been told to limit fluids, for example for a heart or kidney condition, do not drink more or less on your own. Ask how much to drink on hot days; CDC asks clinicians to consider adjusting fluid limits then.
• Warning signs. Which symptoms mean I should call the office, and which mean 911?
• Storage and outages. How should I store each medicine, and what is my plan for refrigerated medicines and powered equipment if the power goes out?
• In writing. Ask for the plan in writing, including when to go back to your usual routine.
• A check-in person. Name someone who will check on you. For people caring for someone at higher risk, CDC suggests visiting at least twice a day.

When to ask. At a routine visit before summer, when a medicine is started or a dose changes, and when a hot spell is forecast. The National Weather Service's experimental HeatRisk forecast rates each day from 0 (green) to 4 (magenta); CDC suggests clinicians plan with patients for orange (2), red (3) and magenta (4) days. For official heat alerts, see Weather watch, warning or advisory: what each alert means for your health.

A pharmacist can answer many of these questions at the counter or by phone; prescription changes still go through your prescriber. A printable version, with room to write your plan, is at Heat-wave medicine questions for your clinician or pharmacist.

Lithium: a closer look

CDC singles out lithium because dehydration can push blood levels into a toxic range. MedlinePlus, from the National Library of Medicine, says to tell your doctor if you develop heavy sweating or fever while taking lithium. Signs of too much lithium can include diarrhea, vomiting, drowsiness, muscle weakness, loss of coordination, blurred vision and ringing in the ears; MedlinePlus says to call your doctor immediately if these appear. Ask your prescriber now what to do about your lithium doses if that happens, and add the answer to your hot-day plan. Otherwise, MedlinePlus says not to stop lithium without talking to your doctor.

Insulin, diabetes pills and supplies

CDC's diabetes program notes that high temperatures can change how your body uses insulin, so you may need to check your blood sugar more often. Ask your care team how to adjust if your readings change. Heat can also damage glucose meters, test strips and insulin pumps.

The U.S. Food and Drug Administration (FDA) gives this insulin storage guidance (current as of September 28, 2026):

• Unopened insulin kept in the refrigerator, at about 36°F to 46°F, works until its expiration date.
• According to U.S. manufacturers' labels, insulin vials and cartridges, opened or not, may be kept unrefrigerated between 59°F and 86°F for up to 28 days. Some products differ (one once-weekly insulin pen allows up to 12 weeks below 86°F), so check your product's label.
• The longer insulin is exposed to extreme heat, the less effective it becomes. Keep it out of direct sunlight and away from heat. Do not use insulin that has been frozen.
• Insulin in a pump that has been exposed to temperatures above 98.6°F should be thrown away.
• In an emergency with no replacement, you might still need to use insulin stored above 86°F. Watch your blood sugar closely, replace the insulin as soon as you can, and do not go without insulin.

When you travel, CDC says to keep insulin in a cooler but not directly on ice or a gel pack. Do not leave insulin, diabetes pills or supplies in a hot car or in direct sun. If you are not sure whether heat damaged your insulin, ask your pharmacist or call the manufacturer's number on the package.

Storing other medicines in the heat

• Read the label. Many labels, including those for the EpiPen and for Ventolin HFA (an albuterol inhaler), say to store at 68°F to 77°F, with short periods between 59°F and 86°F allowed.
• Keep medicines out of cars. CDC asks clinicians to tell patients not to leave medicines in a car or anywhere that gets very hot.
• Epinephrine auto-injectors. CDC says heat may make them malfunction or deliver less medicine. The EpiPen label says not to keep it in a glove box or trunk, or in the refrigerator. Check the viewing window regularly: replace the pen if the liquid is pink, brown or cloudy or has particles.
• Inhalers. CDC says inhalers can malfunction or burst in extreme heat. The Ventolin HFA label warns that temperatures above 120°F may cause the canister to burst.
• Refrigerated medicines that got warm, for example in a power outage: FDA says to check the storage instructions or ask a pharmacist, health care provider or the manufacturer whether the medicine can still be used. A life-sustaining medicine such as insulin may be used until you get a new supply.
• Power outages. FDA suggests keeping a cooler and ice or frozen gel packs on hand for refrigerated medicines. CDC also suggests planning for powered devices such as nebulizers and oxygen concentrators. See A power outage plan for a household that uses medical equipment.

Warning signs of heat illness, and when to call 911

If you take a medicine that reduces sweating, do not count on sweating as an early warning. For everyday prevention, such as water, shade and timing outdoor activity, see Heat-Related Illness: Protecting Yourself in the Central Valley.

In California and the Central Valley

• Cooling off. In California, the state's Heat Ready CA website links to a cooling-center finder and suggests other air-conditioned places, such as public libraries and shopping malls.
• Working in the heat. California employers must take steps to protect workers from heat illness in both outdoor and indoor workplaces. See California's two workplace heat standards.
• Timing. In the Central Valley, ask for your hot-day plan in spring, before the first hot spell.

Sources

1. Heat and Medications – Guidance for Clinicians — Centers for Disease Control and Prevention, first published July 17, 2024; last reviewed September 18, 2025.
2. Heat and Chronic Conditions — Centers for Disease Control and Prevention, last reviewed June 25, 2024.
3. Managing Diabetes in the Heat — Centers for Disease Control and Prevention, last reviewed January 3, 2024.
4. Information Regarding Insulin Storage and Switching Between Products in an Emergency — U.S. Food and Drug Administration, content current as of September 28, 2026.
5. Safe Drug Use After a Natural Disaster — U.S. Food and Drug Administration, content current as of September 1, 2026.
6. EpiPen and EpiPen Jr (epinephrine injection) labeling — DailyMed, National Library of Medicine (manufacturer labeling), accessed October 22, 2026.
7. Ventolin HFA (albuterol sulfate) inhalation aerosol labeling — DailyMed, National Library of Medicine (manufacturer labeling), accessed October 22, 2026.
8. Lithium — MedlinePlus, National Library of Medicine, last revised April 15, 2017.
9. Ibuprofen — MedlinePlus, National Library of Medicine, accessed October 22, 2026.
10. Heat-Related Illness — National Weather Service, accessed October 22, 2026.
11. Heat-related Illnesses — National Institute for Occupational Safety and Health, CDC, March 3, 2026.
12. NWS HeatRisk — National Weather Service Weather Prediction Center, accessed October 22, 2026.
13. Heat Ready CA — State of California, accessed October 22, 2026.
14. Heat Illness Prevention Guidance and Resources — Cal/OSHA, California Department of Industrial Relations, accessed October 22, 2026.
15. Heat-Related Illnesses (fact sheet) — Centers for Disease Control and Prevention, accessed October 22, 2026.