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Are there any concerns or considerations?

The potential risks of oral menthol application in the heat are not yet fully understood. The following risks have, so far, been identified:

Table 1: Potential Risks of Internal Menthol Use

Concern

Toxicity

  • Estimated lethal dose for menthol in humans as low as 50-150 mg/kg BM (equivalent to 3 g for a 60 kg individual).9 This volume is equivalent to 15 x 25 g bags (contains approximately 20 lozenges providing 10 mg total menthol per lozenge) of Original Fisherman’s Friend® (Extra strong, white packet).

Unsuitable Dose

  • Risk of confusion around suitable doses/concentrations of L-Menthol use.
  • It is recommended that athletes use existing commercial products rather than sourcing raw ingredients.

Inadvertent Doping

  • All orally ingested supplements pose a risk of cross-contamination.
  • It is recommended that the athletes use commercially available L-Menthol-containing products from well-known food/confectionary companies, and in the case of sports nutrition supplements, that these be batch tested.

Performance

  • Risk of mis-pacing since menthol is capable of mis-representing real-time thermal information to the brain.

Thirst Sensation

  • Menthol may attenuate thirst, potentially leading to deception-driven dehydration. Hydration should be monitored closely amongst athletes where hydration is key to maintaining performance or for very heavy sweaters.

Manual Handling

  • Pure menthol causes skin irritation and hence, is labelled as ‘Hazardous’ when handling raw materials.
  • It is recommended that athletes source existing commercial products rather than sourcing raw ingredients.

Limitations to the current evidence supporting menthol use

High-Performance Environment

  • Studies among elite athletes, particularly in events that are representative of real-world performances and conditions (e.g., the degree of thermal discomfort tolerated, motivation for success/resist fatigue) is of high priority.

Sex

  • L-menthol research has largely been conducted on male cohorts who are recreationally active or trained. It is not known whether the subtle alterations in sub-elite populations will translate to measurable outcomes for elite athlete in the field.3
  • Research on female participants is to be encouraged because of identified sex-differences in olfaction and trigeminal sensitivity.10

Sports/Activities

  • More research is warranted on the effects of L-Menthol, on performance of intermittent, dynamic and explosive activities, fine motor movements, or team-based competitive sports due to insufficient research in the field.3

Safety

  • To our knowledge, there are no recorded instances of heat-related illness in experiments involving the internal application of L-menthol. Such experiments are ethically bound by strict withdrawal criteria and therefore, careful thermal monitoring during athletic events in less-controlled environments is necessary.

Individual Responses

  • Inter-individual difference in response to L-menthol mouth rinsing may be distinguished by the calculation of an individual’s menthol sensitivity index.11
  • A clear dose-response has yet to be identified. Individual approaches are warranted above pursuing a ‘more is better’ approach.

Diminishing Returns

  • Further understanding of single or repeated mouth rinsing and the reasons for habituation (i.e., diminished response to the repeated application of menthol dose) need to be clarified.

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