Background Determining the post-mortem interval (PMI) through examination of insect activity on deceased bodies is essential in forensic science. Establishing the time of death in cases involving drug ingestion can present difficulties for law enforcement, complicating evidence collection. In unnatural death investigations, a forensic pathology approach is commonly employed, focusing exclusively on samples obtained from the body, which can lead to biases and errors, particularly beyond 72 hours after death. Notably, no research on insect colonization and succession on cadavers has been conducted in Kenya, despite a growing number of unidentified deaths. This research aimed to identify and assess forensically significant insects and to establish the effect of flunitrazepam (Rohypnol®) on carrion-insect successional patterns on pig carcasses. Methods Four domestic pigs, averaging 24.8 kg, were used, with one designated as the control and three assigned as the experimental group. The experimental pigs received oral drug administration mixed with 250ml of vodka to simulate drink spiking in a bar. Subsequently, the pigs were euthanized, and their carcasses were placed in cages. Adult insects and flightless adult invertebrates were sampled daily until the dry remains stage of decomposition. Existing insect identification keys were utilized for species identification. Results The results revealed consistent insect succession patterns across the four carcasses. The mean number of insects across developmental stages decreased as flunitrazepam dosage increased. However, no significant variation among the carcass groups was observed in insect genera. Decomposition was categorized into five stages: fresh, bloated, active decay, advanced decay, and dry, consistent with prior studies. Insect succession included Diptera (e.g., Chrysomya spp., Lucilia sericata), Coleoptera (e.g., Dermestes maculatus), and Hymenoptera (e.g., Camponotus sericeus), with Calliphoridae being most abundant. The flunitrazepam-ingested carcasses showed prolonged decomposition stages compared to control. Conclusion These findings highlight the need to consider drugs like flunitrazepam in forensic entomology analyses.