Experimental setup
OLP
BLIND
A randomized parallel group experimental design was used with participants randomly assigned to one of the four groups (active OLP nasal spray, passive OLP nasal spray, passive OLP capsules, natural history). Block randomization was conducted by the principal investigator prior to the laboratory session to allocate participants equally to all groups using a random number generator. Experimenters, who enrolled and assigned participants were not blind to group allocation (nasal spray vs. capsule vs. natural history) but blinded to active vs. passive nasal spray.After giving informed consent, participants were asked to fill out the baseline measures on a PC in the laboratory. Next, all participants received the same highly standardized information about the OLP rationale (see OLP rationale above). Participants were then informed about their group allocation and participants in each of three OLP groups received the OLP capsules or nasal spray, accordingly. The investigator handed over the nasal spray or the capsules (wearing rubber gloves), gave exact instructions on how to use the spray or the capsules and supervised the intake of the first of the seven doses. Participants in the OLP groups were then instructed to take the OLP capsules or nasal spray at home on the following six consecutive days. To enhance adherence, participants were also asked to fill out a paper and pencil protocol (including the day and time of OLP intake). Participants in the natural history group underwent the same procedure without receiving placebo treatment. After 7 days, all participants were invited via email to fill out the post-intervention measures online on study day 8, i.e., one day after the last OLP intake (see Fig. Experimental design.