A swish of minty water can make a 35 C ride feel noticeably cooler. It doesn’t make your body any cooler, and the best recent evidence says it may not make you faster either.
That’s a harder sell than the marketing. So here’s the straight read on what menthol mouth rinsing does, who it might help, and how to test it before race day.
What the Evidence Says About Menthol Mouth Rinsing
Early studies looked great. The newest big review does not.
The 2024 meta-analysis in Sports Medicine - Open pooled 10 studies and 153 participants. It found a standardized effect of 0.12 (95% CI -0.08 to 0.31, p = 0.23). The confidence range crosses zero. In short: the average effect is too small to tell apart from nothing.
An earlier review of 13 studies had found a borderline benefit (Hedges g = 0.33). The gap between 0.33 and 0.12 is the story.
Two cautions. The authors rated the evidence as very low certainty, and none of the 10 studies had a low risk of bias. Also, a test for small-study bias was positive (p = 0.01). Small, flattering studies tend to get published, which inflates the average.
The 2024 authors reported that concentration, swill length, sex and air temperature did not significantly change the result. No one setup stood out as the winner.
Menthol isn’t useless. It’s unproven.
How Menthol Works: It Fools the Thermostat
Menthol switches on TRPM8, the receptor in your mouth that detects cold. Your brain gets a “cool” message. Your body temperature stays the same.
Think of taping over the engine temperature light on a dashboard. The engine runs just as hot. You just stop seeing the warning.
The numbers back this up. A pooled analysis of 17 trials found thermal sensation dropped (weighted mean difference -1.65), while core temperature moved by only 0.02 C. In the original 2010 cycling trial, rectal temperature rose about 1.7 C in both the menthol and placebo conditions. Translation: you feel cooler, but you’re cooking at the same rate.
Why might that help anyway? Your brain slows you down partly based on how hot it feels. Quiet the signal and you may push a bit harder. That’s the theory behind the 8-of-9 riders who lasted longer in the 2010 trial, with a +9% gain in endurance capacity.
It’s also the risk.
Where the Single Studies Land
Some trials are strong. Some are flat.
| Study | Test | Heat | Result |
|---|---|---|---|
| Mundel & Jones 2010 | Ride to exhaustion | 34 C | +9% (8 of 9 riders longer) |
| Stevens 2016 | 5 km treadmill run | 33 C | 25.3 min vs 26.0 min control |
| Jeffries 2018 | Ride to exhaustion, late rinse | 35 C | +82 s menthol vs +15 s placebo |
| Best 2021 | 40 km cycling time trial | 32 C | No significant difference |
| Crosby 2022 | 3-minute all-out ride | 33 C | No change in absolute power |
Stevens also compared ice slurry. Ice lowered core temperature by about 0.3 C but didn’t improve the run time or the feeling of heat. Menthol did both. That supports the idea that perception, not physiology, drives the benefit.
Most of this work is short, small (often 8 to 16 people), and done on young men in labs. Very little exists on events longer than about an hour. If you race an Ironman bike leg, you’re extrapolating.
Menthol vs Carbohydrate Rinse in Long Races
If you’re racing for hours, fuel matters more than feel. The Best 2021 trial had cyclists rinse with menthol, carbohydrate, or both during a 40 km time trial at 32 C. The result: no significant difference, and no added benefit from combining them. Menthol alone trended slower than the carbohydrate rinses.
Menthol also cut thirst. That sounds nice until you remember thirst is your drinking cue.
Don’t trade sugar or fluid for mint.
Dose, Protocol and Risks
More isn’t better. A 2024 dose study found the best range was 0.01% to 0.1% l-menthol. At 0.5%, work output fell about 10% because of mouth irritation.
| Concentration | Work output change | Note |
|---|---|---|
| 0.01% | about +5% | Most-used dose |
| 0.1% | about +3% | Still in the sweet spot |
| 0.5% | about -10% | Irritating, avoid |
The Australian Institute of Sport suggests 0.1 to 0.5 g of l-menthol crystals per liter of water (0.01% to 0.05%), swilled for 5 to 10 seconds every 5 to 10 minutes. Late-race rinses also showed promise. Even so, raw crystals are risky. The AIS puts a lethal dose around 50 to 150 mg/kg, roughly 3 g for a 60 kg adult. Use a commercial product, not a kitchen scale.
Other risks to know:
- Mis-pacing. You feel fine while your body keeps heating up.
- Dulled thirst. Drink on a schedule.
- Habituation. The cool feeling may fade with repeated use.
One more point. There’s no true placebo. Mint and menthol both trigger TRPM8, and athletes smell the difference. Study blinding was flawed in 92.3% of the trials in the 2024 review. So some “benefit” may be expectation. For you, a felt benefit still counts, as long as pacing stays honest.
On rules: don’t assume anything. Check your exact product on GlobalDRO and the current WADA list before you race.
A Case Study: Testing It in Training
Here’s an illustrative example, not a real athlete. Picture a runner named Dana. She’s 41, training for a 70.3 in Texas in June, and running about 35 miles a week. Her long runs in August heat felt brutal around the 90-minute mark.
She ran four similar hot long runs at the same easy pace. Two used a commercial 0.01% menthol rinse every 10 minutes after the first hour. Two used plain water. She logged how hard each run felt out of 10 and tracked her heart rate drift.
The rinse days averaged 6.5 out of 10 for effort in the last 30 minutes. The water days averaged 7.5. Her heart rate drifted about the same on both. The rinse made the final hour feel easier while her body stayed equally taxed. Her takeaway: use it late, hold pace by the numbers, and keep drinking by the clock.
That’s a sample of one. But it’s the right kind of test.
Using the Rinse Without Fooling Yourself
First, build your base heat tolerance. Menthol is a trick. Heat acclimation is a real physiological change. Do that first.
Second, pace by watts or heart rate, not by feel. If menthol shifts feel, numbers keep you honest. Our guide to Zone 2 training covers how to anchor easy effort to the data, and the same logic applies on a hot bike leg. Triathletes can try it in a brick session, where the run off the bike is hottest.
Third, trial it. Same route, same pace, rinse versus no rinse, and write down how it felt. AthleteOS flags heat stress on hot sessions, offers cooling options including a menthol rinse, and logs your perceived effort across heat sessions. Over a few weeks, you’ll see whether it helps you or just feels good.
Cool feelings aren’t cool bodies.