Effect of taste sensation on cough reflex sensitivity.

Cough is among the most common symptoms with which people present for medical attention, but evidence-based treatments remain limited. One issue compromising interpretation of clinical trials of cough preparations is that control formulations often are nearly as effective as those that contain active ingredients. This observation has caused some researchers to propose that one or more nominally inactive ingredients may have some physiological effects. For example, most liquid cough preparations are highly sweetened, and it has been suggested that sweet taste might modulate cough sensitivity. The fact that honey has been used for thousands of years as a cough remedy is consistent with this idea. However, empirical evidence for modulation of cough sensitivity by taste was lacking. Evidence is still sparse, but relevant experiments have now been published: rinsing the mouth with a sweet sucrose solution increased cough thresholds in a single-inhalation capsaicin challenge. Furthermore, rinsing the mouth with a bitter solution did not affect thresholds, an important demonstration of specificity. The underlying mechanisms of cough suppression by sweet taste are still unclear. However, extant data suggest that modulation of cough sensitivity by taste is a promising area for further investigation. Such work may lead to greater understanding of apparent placebo effects in clinical trials and provide empirical support for therapies based on stimulation of taste nerves.