A pre-trial evaluation of blinding for a Chinese herbal medicine trial

Blinding is considered an important methodological characteristic in clinical trials to minimise bias and maximise the validity of a trial. Unlike pharmaceutical substances, most herbal medicines have distinctive sensory specifications, including odour and taste, which can be quite challenging when developing a placebo control to match the specific characteristics of herbal substances being examined. The present study was, therefore, designed to evaluate whether the participants could differentiate an active herbal capsule (Ganopoly combination) from a placebo material capsule. The aim of this study was to develop a suitable placebo substance for encapsulation to be used in a future herbal medicine clinical trial.

The current study was improved upon the previous investigation, and several modifications were made to the placebo substance in order to mimic the herbal substance characteristics. Prior to conducting the study, a refined placebo substance was developed using commonly consumed culinary agents. Sixty-two healthy volunteers participated in the study and were randomly provided one of the two substances. Individuals were asked to evaluate the three sensory characteristics of the allocated capsule (visual appearance, odour, and taste), and determine whether they believed the substance to be a 'herbal' or a 'placebo' substance.

The study provided evidence on the success of blinding for only two sensory characteristics, namely, visual appearance (95% CI -0.15, 0.34) and odour (95% CI -0.34, 0.15). In contrast, the findings related to the taste indicated that participants correctly guessed the herbal substance compared to the placebo substance to a significantly higher proportion than would have been expected by chance alone (95% CI 0.14, 0.60).

The failure to blind participants for taste highlights the difficulties in preparing placebo herbal substances that match as closely as possible to a real herbal substance. Blinding is particularly challenging where herbal medicines have different sensory characteristics.