Caffeine Before Exercise in Hot Weather: Performance, Core Temperature and Safety

Coffee before a workout is a habit for many athletes, and for good reason: caffeine is one of the best-studied performance aids. But does the same advice hold when it is 95°F (35°C) outside? The research on caffeine before exercise in hot weather is more mixed than the research in cool conditions. A 2022 meta-analysis found a small endurance benefit and only a trivial rise in core temperature, while a 2024 trial found no benefit and more heat strain.

Here is what those studies actually measured, how to read them, and a practical plan if you train or race in the heat.

Key takeaways

• A meta-analysis of 13 studies found that caffeine improved endurance performance in the heat by about 2% on average, with a small, likely trivial, effect on core temperature.
• A 2024 controlled trial using 5 mg per kg found no performance benefit in 35°C heat, plus higher core temperature, more sweating and worse thermal comfort.
• Studies used fairly high doses (3 to 9 mg per kg). Lower doses have barely been tested in the heat.
• In hot conditions, start low, prioritize hydration and cooling, and treat caffeine as optional rather than essential.

In this article

1. Why heat changes the question
2. Caffeine before exercise in hot weather: what studies show
3. How much caffeine, and when
4. A practical hot-weather plan
5. FAQ

Why heat changes the question

In cool conditions, caffeine’s performance effects are well established: it reduces the perception of effort and helps you sustain intensity. In the heat, your body is already working hard to dump heat through sweating and increased blood flow to the skin. Any factor that raises heat production or reduces heat loss could, in theory, push core temperature up faster and cut performance short.

Caffeine slightly increases metabolic rate, which is why researchers have asked whether it adds to heat strain. The answer depends on the study.

Caffeine before exercise in hot weather: what studies show

The meta-analysis: a small benefit, a trivial temperature effect

Researchers led by Naulleau and colleagues, including sports nutrition researcher Louise Burke, pooled studies on caffeine and endurance exercise in the heat. The review was published in Sports Medicine in 2022. In the preprint version, the analysis included 13 studies with 212 physically active to well-trained participants, mostly given 3 to 9 mg of caffeine per kg of body weight about an hour before exercise.

• Performance: caffeine improved endurance performance by about 2% on average (based on six studies), which the authors considered practically worthwhile.
• Core temperature: caffeine increased the rate of rise in core temperature by about 0.1°C per hour, which the authors judged trivial. After adjusting for possible publication bias, the effect became smaller and no longer statistically significant.

The 2024 trial: no benefit and more heat strain

A double-blind, randomized crossover study published in the European Journal of Applied Physiology in 2024 tested 12 caffeine-habituated men cycling to exhaustion at 35°C (95°F) and 40% humidity, one hour after taking 5 mg per kg of caffeine or a placebo.

The authors concluded that the dose did not help performance and increased thermal strain, and they raised safety questions for recreational athletes competing in the heat. They also noted limits: a small, all-male sample, participants who were not heat-acclimated and no fan cooling.

How to read the two together

These findings are not as contradictory as they look. The meta-analysis shows an average effect across varied protocols, some with cooler-feeling conditions or acclimated athletes. The 2024 trial represents a harsher scenario: steady cycling without airflow in strong heat. A reasonable takeaway is that caffeine can still help some people in the heat, but the margin is smaller, the extra heat load is real in some conditions, and individual response matters more than usual.

How much caffeine, and when

Most heat studies used 3 mg per kg or more. For context:

Those amounts are higher than many people realize, and they bump against general safety reference points. The FDA and EFSA consider up to 400 mg per day safe for most healthy adults, and EFSA considers single doses up to 200 mg safe. EFSA recommends no more than 200 mg per day during pregnancy and breastfeeding, and caffeine is discouraged for children and teens. The 2024 authors suggested lower doses might give a benefit without the heat cost, but that has not been properly tested yet.

Timing in the studies was about one hour before exercise. For a deeper look at timing, see our guide on how long caffeine takes to work.

A practical hot-weather plan

1. Test in training, never on race day. Try your caffeine plan in conditions similar to your event.
2. Start low. A regular cup of coffee is a sensible first step rather than a high-dose supplement.
3. Hydrate before you start. Moderate coffee intake is not the dehydration trap it is often made out to be; our article on whether coffee dehydrates you explains why. In heat, your sweat losses are the bigger issue.
4. Cool down in advance. Cold drinks, shade, light clothing and training early or late in the day help more than any supplement.
5. Acclimatize. Body adaptations to heat over one to two weeks of gradual exposure make the biggest difference to how you cope.
6. Watch for warning signs. Dizziness, headache, nausea, confusion or stopping sweating are reasons to stop, cool off and seek help.
7. Skip it if you are sensitive. If caffeine makes you jittery or raises your heart rate noticeably, the heat will not make that better.

Competing? Check your sport’s rules on supplements. Caffeine itself is not prohibited by WADA, as we explain in is caffeine banned in sports?

Coffee for summer training

If you do drink coffee before a hot session, an iced brew is more pleasant than a steaming mug. Our Cold Brew Coffee is coarse ground for smooth, low-acid cold brew you can portion precisely. If you want a smaller caffeine dose without giving up the ritual, Half Caf blends regular coffee and water-process decaf for half the caffeine. On cooler days, athletes who want a stronger lift often reach for Max Caf Blend, our high-caffeine Tanzanian and Indian Robusta blend, but in strong heat, a lighter cup is the more cautious choice.

Caffeine and heat FAQ

Does caffeine raise body temperature during exercise?

It can, slightly. A meta-analysis found only a trivial effect on the rate of core temperature rise, while a 2024 trial at 35°C measured mean core temperature about 0.2°C higher with 5 mg per kg.

Is it safe to drink coffee before running in hot weather?

For most healthy adults, a normal cup is unlikely to be a problem, but research suggests high doses add some heat strain. Keep the dose modest, hydrate and cool well. Ask your doctor if you have a heart condition or other health concern.

Does caffeine still improve performance in the heat?

On average, slightly: about 2% in the pooled studies. But at least one well-controlled trial found no benefit, so individual testing matters.

Does caffeine make you sweat more?

In the 2024 study, whole-body sweat rate was about 21% higher with caffeine, which also means you need to replace more fluid.

What is the best time to drink coffee before a hot workout?

Studies typically used about 60 minutes before exercise. Earlier morning sessions also avoid the hottest part of the day.

Sources

1. Naulleau C, et al. Effect of Pre-Exercise Caffeine Intake on Endurance Performance and Core Temperature Regulation During Exercise in the Heat: A Systematic Review with Meta-Analysis, medRxiv preprint 2021; published in Sports Medicine, 2022.
2. Publication record for the Sports Medicine meta-analysis, Australian Catholic University Research Bank.
3. John K, et al. Caffeine ingestion compromises thermoregulation and does not improve cycling time to exhaustion in the heat amongst males, European Journal of Applied Physiology, 2024.

Facts checked in October 2026.

This article is for general information only and is not medical advice. If you have a health condition, are pregnant or take medication, ask your doctor before changing your caffeine intake.

Keep reading: Caffeine for HIIT · How Much Caffeine Is Too Much? · Best-selling coffees