After psychedelics were banned in 1968, the flourishing research on the use of psychedelics in patients with a mental disorder stopped abruptly. Recently, we see a renaissance of this research.<br/> AIM: To present an overview of what is known about the treatment of addiction and psychosis with psychedelics.<br/> METHOD: Literature study based on Medline en PubMed publications till December 2019.<br/> RESULTS: Studies on the effectiveness of psychedelics in the treatment of addiction and psychosis is still very limited in size and methodological quality. Nevertheless, most studies show positive effects of both classical and atypical psychedelics in a variety of addictions on motivation, craving, reduced consumption, and abstinence often following a single dose and with long-lasting benefits (3-24 months). Use of ketamine in patients with a psychosis stabilized on an antipsychotic might reduce negative symptoms.<br/> CONCLUSION: Before psychedelics can be used in standard clinical practice for the treatment of patients with an addiction or a psychosis, larger and methodologically better studies are needed. The use of psychedelics also creates an opportunity to better understand the shared underlying pathology of many different mental disorders.