The insect successional wave is a primary method to estimate the time elapsed since death. Several studies have shown that antemortem consumption of opioids affects maggot growth rates. However, there are no published data that investigate the effect of antemortem opioids uses on successional patterns. Therefore, the purpose of this research was to investigate the effect of methadone on the successional patterns of insects on rabbit carcasses. During this successional study, 15 and 12 insect taxa were recorded on carcasses for 15 d sampling intervals during spring and winter 2018, respectively. Chrysomya albiceps and Calliphora vicina were the most frequent fly species. These two species preferred to lay eggs on the control carcasses earlier than the treated carcasses. Lucilia cuprina was observed exclusively on the remains of untreated carcasses, while Saprinus chalcites was recorded only from the remains of treated rabbits. Permutation analyses based on the Mantel test for the similarity values of taxa between treated and untreated carcasses in the spring and winter were 0.64 (P = 0.009) and 0.69 (P = 0.003), respectively. Permutation analyses for the two most dominant fly species between the treated and untreated carcasses in the spring and winter were 0.51 (P = 0.05) and 0.49 (P = 0.09), respectively. The results revealed that the overall pattern of insect succession was similar between the treated and untreated rabbit carcasses. However, the patterns of succession of Chrysomya albiceps and Calliphora vicina were slightly different between both treated and untreated carcasses and this could have an influence on the PMI estimation.