Introduction:Paracetamol (Acetaminophen) in addition to aspirin is the most commonly used analgesic and antipyretic medication by millions of patients worldwide. It is an example that paracetamol as medicine that in the world is provided without a doctor’s prescription, can lead to death. Today paracetamol became an integral part of a heroin mixture and is very popular at the street market. The main reason for this is that it can be obtained without a prescription, it is cheap, and by most people well tolerated without side effects. It is probably used for “cutting” the pure heroin, as it says in the jargon, and in that manner from small amount of pure drug is obtained greater amount, which is then sold on the street. The goal is to identify presence of paracetamol, by analytical method of gas chromatography mass spectrometer (GC-MS) in postmortem material together with psychoactive substances.Material and methods:For chemical-toxicological analysis is used biological material collected trough autopsy of 20 deceased people, suspected to have died due to psychoactive substance overdose. All received samples are stored at -20 ° C until analysis at our laboratory. From processed 47 samples that were analyzed in the period from 2014 to 2015, 19 are blood samples, urine 19, 3 samples of stomach contents, and 6 samples of bile content. Deceased were middle-aged, of which only 7 were female. The tested samples were processed according to two methods of extraction. Extraction by XAD-2 resin, and the extraction by the method of salting out with sodium tungstate. Extracts of the samples were then dissolved in chloroform and continued analysis at the analytical instrument. Identification of the paracetamol presence, in the test biological samples is demonstrated by the technique of gas chromatography with mass spectometry (hereinafter referred to as GC-MS). The technique of GC-MS is a selective, sensitive and reliable, and is therefore considered a “gold standard” for determining the drug, and the drug substance. Used GC-MS instrument was an Agilent 7890A with helium as the carrier gas.Results:The analysis of blood samples, urine, bile and stomach contents, obtained after the autopsy of deceased persons, by using gas chromatography with mass spectrometry, in analytical manner confirmed the fact that paracetamol is a very common component of psychoactive substances poisoning. In our assay of samples we detected psychoactive substances (heroin, codeine, morphine, sertraline, diazepam), and almost all were found in the combination with paracetamol, indicating the poor quality of illicit drugs sold on the market.Discussion:Paracetamol (Acetaminophen) is a very common component in mixtures of street drugs. Such mixtures almost anyone can afford, but the very quality of these drugs has become extremely low, because it does not sell the pure substance, but is mixed with various medications. According to research Pantazia et al. the heroin mixture proportion of the heroin is very small so a lot of that mixture has only 3% of heroin, a large number of cases can be only 1% of pure heroin. Most of the time it replaces caffeine and paracetamol. According to the Risser et al. reason why acetaminophen component is present in these mixtures is because it can be purchased without a prescription, it is cheap, well tolerated by most people and shows no side effects.Conclusion:When we talk about illegal drugs, we must emphasize the fact that there is no quality control, or the composition of the drug. The composition of the drug purchased on the black market is still unknown to potential user. While reaching the final drug users it pass through many hands, and at each step something is added to increase earnings. Most often present additives or impurities in narcotic drugs that are added are caffeine, ephedrine, acetaminophen, acetylsalicylic acid (aspirin) and additives such as powders, cement and chalk.