The present invention provides a rapid, sensitive method for forensic drug testing in a post-mortem subject using oral fluid collected from the post-mortem subject. The method comprises collecting a sample of oral fluid from a post-mortem subject, analyzing the oral fluid sample qualitatively to detect the presence of one or more non-naturally occurring drugs, analyzing the oral fluid sample quantitatively to determine concentration of the one or more non-naturally occurring drugs in the post-mortem subject, and identifying the one or more non-naturally occurring drugs in the post-mortem subject. The detection and quantification in oral fluid is more sensitive and faster than detection and quantification of the non-naturally occurring drugs in blood, urine, bile, and liver tissue collected from the same post-mortem subject. Further, the qualitative and quantitative results are obtained in as little as three hours.