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The objective of this study was to determine the effects of a placebo treatment on cough in patients with cough associated with acute upper respiratory tract infection (URTI).Patients with dry or slightly productive cough associated with a history of URTI were recruited. Cough frequency (CF) over 15 minutes was recorded by means of a microphone connected to a pen recorder. Cough suppression time (CST) was recorded when patients were instructed by means of a red light to try not to cough. Patients received either a single dose of vitamin E (placebo treatment) or no treatment. CF and CST were recorded before and 15 minutes after treatment.Twenty-seven patients were randomized to placebo treatment and 27 to the no-treatment group (mean age 22.6 years). The median difference between post- and pretreatment CF was −3 in the no-treatment group and −18 in the placebo group (p = .0003). There was a significant increase in CST in the placebo group compared with no treatment (p = .027).The results demonstrate that placebo treatment has significant antitussive activity. This placebo effect may be related to generation of central neurotransmitters such as endogenous opioids.CF = cough frequency; CST = cough suppression time.