This paper presents historical use of substances from the class of psychedelics, their main pharmacological characteristics that are based on a large number of preclinical and clinical studies and the results of recent clinical studies. Classical serotonin psychedelics, presumably by acting via 5-HT2A receptors, have shown a positive effect in the treatment of mental illnesses such as depression, anxiety, obsessive-compulsive disorder, autism and addictions like alcoholism and nicotine addiction. The paper presents some basic, assumed mechanisms by which psychedelics achieve positive therapeutic effects, as well as their advantages and disadvantages compared to conventional therapy. However, despite great advances in research, knowledge about the exact mechanisms of therapeutic action of psychedelics is still insufficient. By further research it remains to examine the exact pharmacodynamic profile in order to determine exactly which psychedelic works best in which indication, in what dose it should be used and what are the risks of long-term use, especially for certain risk groups of patients. These discoveries paved the way for the development of new more effective and safer therapeutic options for various mental illnesses in order to provide patients with the best possible therapy and a higher quality of life.