Background:Motilin plasma concentrations are positively correlated with hunger ratings during the fasting state. Moreover, the motilin agonist erythromycin stimulates meal requests. Objectives:The first aim of the study was to evaluate the effect of erythromycin on ad libitum food intake. The second aim was to study the involvement of endogenous motilin and octanoylated ghrelin on voluntary meal initiations. Design:Study 1: Fourteen healthy participants were studied twice after an overnight fast. Intravenous administration of placebo (saline) or erythromycin (40 mg) was given in a double-blind randomized order. Participants had the opportunity to eat ad libitum from an excess free-choice buffet (2330 kcal) for the duration of 1 h. The primary outcome was total caloric intake. Study 2: Thirteen healthy participants were studied after an overnight fast. Baseline blood samples were collected before a breakfast (245 kcal). After a rest period of 90 min, blood samples were collected every 15 min for a duration of 5 h. During this period, volunteers could request small meal portions (164 kcal/serving) at time points of their choosing and unlimited in numbers. The primary outcome was the determination of plasma concentrations before postbreakfast spontaneous meal requests. Results:Ad libitum food intake did not differ between placebo and erythromycin groups (difference compared with placebo: 79 kcal; 95% CI: -245.9, 403.97 kcal; P = 0.3). Octanoylated ghrelin concentrations before spontaneous meal requests were, on average, 36% (95% CI: 5.8%, 65.7%; P = 0.02) higher than values before breakfast, whereas motilin concentrations did not increase (6% increase: 95% CI: -5.9%, 17.2% increase; P = 0.3). Conclusions:Motilin receptor stimulation during the fasting state does not affect total caloric intake nor does endogenous motilin stimulate meal requests after breakfast in the current study population. This trial was registered at www.clinicaltrials.gov as NCT03024879.