FIG. 1.

Circadian rhythm of cough frequency in groups of cold sufferers studied for 24 hours before and 36 hours during treatment with placebo or guaifenesin (400 mg) syrup four times daily at 6-hour intervals. Cough frequency is greater in the morning and afternoon than overnight. Sloping line depicts average rate of decline in cough frequency over 60 hours around which 24-hour variability is manifested. (Redrawn from Kuhn JJ, Hendley JO, Adams KF, et al. Antitussive effect of guaifensein in young adults with natural colds. Chest 1982;82:713-8.)