Objectives: The objective of this paper is the literature review to determine which drugs lead to false positive results of toxicological analysis and which functional groups are responsible for cross reactions and false positive analysis. Elaboration of the topic: The abuse of drugs and certain medical products is a major social and health problem today, which is why the number of different drug tests has increased over time. In order to determine the presence or absence of illicit substances in the body, analyzes of biological samples are performed. Screening tests confirm only the possibility of the presence of drugs in the sample. False positive results represent all those results that show the presence of an absent state in reality. The most common cause of false-positive test results are cross reactions. Considering the number of drugs developed so far, it can be concluded that there is a possibility of similarity of the three-dimensional shape of some of these drugs, or their metabolites, which consequently leads to cross-reactions and false positive results. False positive test results will almost always turn out negative on a confirmatory test. Tests for the detection of synthetic cathinones are still underdeveloped, which refers especially to screening tests. Conclusion: Drugs that cause cross-reactivity with benzodiazepines are sertraline and oxaprozine, with barbiturates ethosuximide and phenytoin, with the cannabinoids efavirenz, pantoprazole and niflumic acid, with the opioids diphenhydramine, doxylamine, quinolone antibiotics, rifampicin, dextromethorphan and amisulpride and with the amphetamines ranitidine, labetalol, chloroquine, methylphenidate and amantadine.