Acute respiratory tract infections (ARTIs) are highly prevalent diseases in primary care and adults suffer from 2?3 ARTIs per year. Although most ARTIs are self-limiting, they may cause significant burden to individuals who frequently seek medical consultation.

A placebo response refers to all health changes resulting from administering an inactive treatment. This includes the regression towards the mean and the natural course of the disease which may introduce strong effects in the placebo group, particularly in self-limiting diseases with comparably short durations such as ARTIs. Hence, clinical trials investigating a medication for this kind of diseases need to demonstrate efficacy by overcoming a strong placebo response.

Individual patient data meta-analyses were performed to assess the response-rates from pooled data of two randomized, double-blind, placebo-controlled trials1,2 investigating the effect of the ivy leaves dry extract EA 575 in adult patients with acute cough. Based on criteria of the German Institute for Quality and Efficiency in Health Care, a decrease of the total bronchitis severity score (BSS) from baseline to treatment end by ?4 points was considered as treatment response.

Reference Treatment n Responder Response rate p*
[1] EA575 88 83 94,3%
Placebo 90 66 73,3% <0,001
[2] EA575 139 129 92,8%
Placebo 70 55 78,6% 0,003

* ?2-test

Despite the combined response-rate of >75% in the placebo group (121/160 patients) suggesting a strong placebo response, the intervention response-rate of >93% (212/227 patients) demonstrated that efficacious medication may overcome strong placebo responses in RCTs.


1. 10.1691/ph.2016.6712