The larvae of necrophagous fly species are used as forensic tools for the determination of the minimum postmortem interval (PMI). However, any ingested drugs in corpses may affect larval development, thus leading to incorrect estimates of the PMI. This study aimed to investigate the effects of diazepam on the development rate of C. albcipes and to evaluate the reliability of this fly species as samples for toxicological analysis. For this purpose, larvae of C. albcipes were reared on rabbit carcasses treated with a lethal dose of diazepam. The development rate of the fly was measured, and samples from carcass tissues and fly stages were analyzed for diazepam. Results indicated that diazepam was detected in all tested carcasses tissues and different stages of C. albcipes; larvae, pupae, and adults confirming the reliability of these specimens for qualitative toxicology analysis. It was found that the presence of diazepam accelerated larval growth by12 h, whereas the pupal stage was not affected. Furthermore, a 12 h interval bias on the total duration of development, from first larval instar to imago, has to be considered if diazepam was present in the corpse.