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.
From the Common Cold Centre (P.C.L.L., M.S.M.J., R.E.), Cardiff School of Biosciences, Cardiff University, Cardiff, UK; and Procter and Gamble Technical Centres Limited (J.D.H., W.H.L.W., K.S.), Surrey, UK.
This research was supported by Procter and Gamble Technical Centres Ltd., Rusham Park, Whitehall Lane, Egham, UK.
Address correspondence and reprint requests to Professor Ron Eccles, Common Cold Centre, Cardiff School of Biosciences, Cardiff University, Cardiff CF1 3US, UK. E-mail: firstname.lastname@example.org
Received for publication July 12, 2004; revision received September 9, 2004.