Antitussive effects of nasal thymol challenges in healthy volunteers

Eighteen healthy volunteers with normal lung function were tested for cough. Before and after nasal administration of thymol (0.025 ml, 10(-3) M) into both nostrils, urge-to-cough, cough threshold, cumulative and total count of coughs per provocation were estimated during standardized and validated capsaicin cough challenge. Nasal thymol challenges induced pleasant olfactory sensation and in 6 out of the 18 subjects also mild cooling sensation. Cough threshold was not influenced when compared with intranasal saline and vehicle challenges (12.5 vs. 13.2 vs. 10.2 μM of capsaicin to induce two or more coughs (C2), respectively), but the total count of coughs after nasal thymol challenge was significantly lower than that obtained after saline or vehicle (19 vs. 20 vs. 14 coughs/provocation, respectively; p<0.05). Importantly, subjects did not report the urge to cough, which appeared to correspond to C2. We conclude that the modulation of cough by thymol is mostly of olfactory origin.