REF-1462 · Moyen et al., 2024 · Journal of Applied Physiology · Paper · PubMed

Is nicotine riskier in the heat?

In 10 nicotine-naive trained men, an overnight 7-mg patch raised core temperature more at 30 °C and blunted skin blood flow; 2 could not finish. No measured power effect. From the abstract.

Main caveat: Abstract only; the saved source is the PubMed record.
limited evidenceMeasured on trained to highly trained athletes

Moyen and colleagues asked whether nicotine worsens exertional heat strain through more heat production or less skin blood flow. Ten nicotine-naive trained men did four trials at 20 °C and 30 °C after overnight transdermal nicotine (7 mg/24 h) or placebo: 60 min of cycling at 55% VO2peak, then a time trial at about 75% VO2peak.

The difference in gastrointestinal temperature rise between nicotine and placebo was larger at 30 °C (0.4 ± 0.5 °C) than at 20 °C (0.1 ± 0.7 °C); mean skin temperature was higher with nicotine (0.5 ± 0.5 °C, P = 0.02), skin blood flow became progressively lower with nicotine (P = 0.01), and mean arterial pressure rose from baseline in all trials.

Time-trial power was 24 ± 25 W lower at 30 °C than at 20 °C, with no effect of nicotine (P > 0.59). Two participants did not finish their 30 °C nicotine trials. The authors conclude that nicotine increases thermal strain and the risk of exertional heat exhaustion by reducing skin blood flow.

Our reading: the mean effect on core temperature is small with a large spread, but two of ten not finishing is what matters to a race decision. It is one small trial in non-users.

Protocol

Participants: n = 10 nicotine-naive trained men, 37 ± 12 years, VO2peak 66 ± 10 mL/kg/min.
Treatment: overnight transdermal nicotine, 7 mg/24 h, or placebo, double blind, crossover.
Test: 60 min at 55% VO2peak, then a time trial at about 75% VO2peak, at 20 °C and 30 °C.
Measures: gastrointestinal and mean skin temperature, skin blood flow, metabolic heat production, mean arterial pressure, time-trial power.
Funding and interests: grants listed by PubMed: World Anti-Doping Agency (12D18TM), NSERC Canada (2023-04492), Canada Research Chairs Program. First author's affiliation is Eight Sleep Inc., New York. No conflict statement in the record.

Key Results

OutcomeResultP
Nicotine minus placebo, rise in gastrointestinal temperature, 30 °C0.4 ± 0.5 °C
Nicotine minus placebo, rise in gastrointestinal temperature, 20 °C0.1 ± 0.7 °C
Mean skin temperature, nicotine vs placebo0.5 ± 0.5 °C higher0.02
Skin blood flowprogressively lower with nicotine; progressively higher at 30 °C than 20 °C0.01; <0.01
Time-trial mean power, 30 °C vs 20 °C24 ± 25 W lower0.02
Time-trial power, nicotine effectnone>0.59
Did not finish the 30 °C nicotine trial: 2 of 10 (20%): one reached the ethical limit of 40.0 °C gastrointestinal temperature, one withdrew with "nausea and chills" at 39.7 °C.
Heat production: the difference between 30 °C and 20 °C was lower with nicotine (P = 0.01); the authors attribute the rise to skin blood flow, not heat production.
Not in the abstract: whether any placebo trial was stopped early beyond the statement about the nicotine trials, how the two non-finishers were handled in the power analysis, and a P value for the 0.4 °C contrast.

Mechanisms

Measured: lower skin blood flow and higher skin and core temperature with nicotine in the heat.
Authors' interpretation: nicotine raises thermal strain by reducing skin blood flow, not through heat production; they note implications for athletes and military groups with high nicotine use, and for screening nicotine use in study designs.
Inference: heat gives the heart a second job, cooling (PHYS-28, established); less skin blood flow narrows a route of heat loss. Whether habitual users adapt is unknown.

Practical Application

Is nicotine riskier in the heat? In 10 nicotine-naive trained men, an overnight 7-mg patch raised core temperature more at 30 °C and blunted skin blood flow; 2 could not finish. No measured power effect. From the abstract.
Racing hot: there is no performance gain to set against this risk here or in the temperate trial REF-1461. Not from this paper; the base's own practice: an athlete who already uses nicotine and races in heat is told about the finding and the fact that it was measured in non-users, and heat acclimation follows SYNTH-04.
Warning signs: nausea and chills at a high core temperature ended one trial; not from this paper; the base's own practice: heat-illness symptoms mean stopping, whatever the cause.
What it does not show: the effect in habitual users or women; pouches, snus or vapes; a time-trial slowdown from nicotine (none measured in those analysed).

Limitations

Abstract only; the saved source is the PubMed record.
Small (n = 10), men only, with SDs as large as the core-temperature effect.
Nicotine-naive: no direct transfer to habitual users, who are the people most likely to be using it on race day.
One route and dose: overnight 7-mg patch.
Two non-finishers from one arm are a signal, not a rate.
Funding and interests: WADA, NSERC and Canada Research Chairs per PubMed; first author at Eight Sleep Inc.; no conflict statement in the record.
How this entry was checked and changed
Why this level

(from the abstract) — a crossover with fewer than 15 participants (rubric B); the abstract gives its methods and main numbers