Menthol is frequently used in over the counter medications for common colds and coughs. It was formerly considered to be under the class of herbal medicine, but identification of menthol receptor (TRPM8) moved it from the class of herbal medicine to the molecular pharmacology. It has been documented that menthol reduces dyspnoea and nasal obstruction via stimulation of nasal cold or flow receptors. It has also antitussive and antiirritative effect. Menthol can also induce adverse reactions such as airway irritation, dyspnoea, chest tightness and potentially respiratory failure, mainly in children. The mechanisms responsible for adverse reactions of menthol are not known completely. The adverse reactions of menthol could be due to its effects on TRPA1 channel, relevant to airway irritation. Higher concentrations of menthol stimulate TRPA1 channel causing airway irritation. It also increases mucus production and at the same time reduces cilliary activity leading to mucus stagnation. As the adverse effects were reported mainly at the night it is supposed that suppressed cough reflex during sleep potentiated by menthol induced cough suppression might be responsible for lack of airway mucus clearing and obliteration of small airways. Adverse effects could also be due to consequences of reflexes induced by the menthol action on trigeminal afferents, like apnoea or bronchoconstriction. Menthol is effective in relieving respiratory symptoms, but cough and cold medications should be used with caution. Recommendations are low concentrations of menthol used locally (intranasal) and not combined with camphor or cineole, as they may have additive effects and should be avoided in children under 2 years. Further data are necessary to completely elucidate potential risks of over the counter menthol medication in children but based on the meta analysis of documented case reports, menthol can be used safely if its contraindications for use are followed as with any other over the counter medications.
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