Peptides may represent potential treatment options for many severe illnesses. However, they need an effective delivery system to overcome rapid degradation after their administration. One possible way to prolong peptide action is to use particulate drug delivery systems. In the present study, thermally hydrocarbonized mesoporous silicon (THCPSi) microparticles (38-53 microm) were studied as a peptide delivery system in vivo. D-lys-GHRP6 (ghrelin antagonist, GhA) was used as a model peptide. The effects of GhA-loaded THCPSi microparticles on food intake (s.c., GhA dose 14 mg/kg) and on blood pressure (s.c., GhA dose 4 mg/kg) were examined in mice and rats, respectively. In addition, the effects of THCPSi microparticles (2 mg) on cytokine secretion in mice after single s.c. administration were examined by determining several cytokine plasma concentrations. The present results demonstrate that GhA can be loaded into THCPSi microparticles with a high loading degree (20% w/w). GhA loaded THCPSi microparticles inhibited food intake for a prolonged time, and increased blood pressure more slowly than encountered with a GhA solution. Furthermore, THCPSi microparticles did not increase cytokine activity. The present results suggest that THCPSi might be used as a drug delivery system for peptides.