Qualitative and quantitative olfactometric evaluation of different concentrations of ethanol peppermint oil solutions

Selection of an adequate placebo is a major problem in clinical trials of E uminz((R)) (10% peppermint oil/ ethanol) which is used topically for the tr eatment of tension-type headache. This randomized, controlled, double-blind , cross-over study was performed to investigate whether there are qualitati ve differences between 10%, 1%, 0.5%, 0.1%, and 0% peppermint oil, Forty-on e healthy subjects participated (age range 21-28 years); they rated both in tensity, and hedonic tone of the stimuli. Verbal descriptions were combined to multiple response sets (MRS). In addition, the trigeminal impact of odo rants was determined. Intensity ratings and MRS 'menthol like' and 'alcohol /solvent' changed with stimulus concentration. However, intensity had no si gnificant effect on hedonics, trigeminal impact, or the number of descripti ve items used, When MRS 'menthol like' and 'alcohol/solvent' were analysed after being weighted with intensity ratings, changes in relation to stimulu s concentration were lost. Thus, the differences between the five concentra tions of peppermint oil were-to their largest part-due to changes in stimul us intensity. Considering the large day-to-day variability of olfactory sen sitivity the present data support the hypothesis that the odour quality of 10% peppermint oil cannot be discriminated from the odour of 0.1%, 0.5%, or 1% peppermint oil when tested on separate days. Copyright (C) 2001 John Wi ley & Sons, Ltd.