Do placebos that elicit side effects influence perceived treatment allocation and enhance the placebo effect for sleep compared with conventional placebos?

Participants will be recruited under the guise of a study testing a new formulation of an antihistaminic drug containing beetroot extract as an antioxidant efficacy booster, but no active treatment is actually delivered. Instead, after one week of baseline measures participants will be randomised to one of three groups: a benign placebo group, an active placebo group, or to a no-treatment control group. Participants randomised to the benign and active placebo groups will be blind towards their treatment condition, and told they are receiving either the antihistaminic drug or placebos. The no-treatment control group will be told that they will not receive treatment and will instead serve as a control group for the natural course of their sleep difficulty and daily symptoms. The placebo capsules will be made of gelatine. The benign placebo group will receive four conventional placebo capsules per day for seven consecutive days containing only lactose fibres as filler material. The active placebo group will receive four capsules per day for seven consecutive days containing each 500 mg of the food colour E 162, i.e. beetroot extract and 250 mg oxalic acid to stabilize and guarantee the absorption of the beetroot extract. The intention of the active placebo is to produce beeturia, i.e. a red-ish colouration of the urine to simulate side effects. Adherence will be assessed using a daily participant diary. Additionally, participants will need to return the capsule container containing all capsules they have not taken at the end of the study.