Abstract: The forensic toxicological analysis involves a variety of samples for drug detection and with technological advancements, the need for targeted sampling increases. Various samples are analyzed after the sample preparation, often by gas chromatography-mass spectrometry (GC-MS). Depending on the drugs (pharmacodynamics and kinetics), there are general scientific predictions about the distribution of drugs in the body [1], but in practice, what will be the positive results in the same extraction method? The objective of this article was to provide another level of biological matrix classification that can affect results in the same sample preparation techniques. This study was performed on about three thousand postmortems of the toxicology laboratory of forensic medicine (Guilan), in three one-year periods (1390, 1396, and 1400), during a decade. Urine, liver, stomach, blood, and bile after liquid-liquid extraction were examined by GC-MS in a general method (HP_5 MS column with initial, final, inlet, and interface temperatures and the rate of temperature, were respectively, 60 ºC, 280ºC, 250 ºC, 280, ºC and 20 ºC min1). The positive responses were determined in each group of samples by studying for drugs, toxins, and their metabolites in the list of about 650 organic compounds (such as medicines, drugs, toxins, etc.) which were already registered in the local software library with a determined retention time and a high match quality (more than 75%). Positive and negative results were recorded and compared by sample type. The results by years were determined and the statistical percentage of positive (desired) results, were as follows; urine, bile, stomach content, liver, and blood in 1390, were respectively 0, 36, 5,54,88, 1n 1390, 11, 25, 50,72, 1n 1396 and 10, 15, 44,49 77 1n 1400 (a total average can be seen in the pie chart, with 36% urine, 26% bile, 21% stomach content, 12% liver, and blood, 5%). In all three research periods, the results showed that the positive answers were related to the following samples: urine, stomach contents, and bile, which were referred to as the "golden triangle of diagnosis”. Each sample has its characteristics, but in the case of some others, this characteristic is more obvious e.g., in urine samples, drugs can be concentrated up to 100 times and the possibility of finding drug metabolites in urine is high. Targeted sampling is not only useful in sample selection in toxicology laboratories but also, spends fewer resources on detection, is cost-effective, and is in line with environmental considerations.