The present study aimed to investigate the stability of morphine, morphine-3-β-glucuronide (M3G), morphine-6-β-glucuronide (M6G), 6-acetylmorphine (6-AM) from heroin metabolites, and codeine, codeine-6-glucuronide, nor-codeine, fentanyl, norfentanyl, paracetamol, caffeine from its adulterants at room temperature for 24 hours in order to understand the effect of instability in postmortem redistribution (PMR). The heroin metabolites and adulterants were spiked into the control blood sample with the standard addition method. Then they were kept at room temperature for 4 hours and 24 hours and the blood samples were prepared by liquid-liquid extraction method. The prepared samples were analyzed using the validated analytical method with a liquid-chromatography-tandem mass spectrometry. According to the results of this study, no significant changes were observed in the analyte concentrations in the 4- and 24-hour postmortem blood, and it is thought that the other mechanisms may be more responsible than the instability of analytes for the significant concentration changes in PMR.