Background and aims: Ingestion or administration of classic psychedelics is sometimes associated with improvements in well-being or mental health. Acute mystical-type experiences that psychedelics occasion have been suggested to be related to such improvements. Meanwhile, other features of the psychedelic experience, such as psychological insights and emotional breakthroughs, are also increasingly being studied. This review aimed to collect and assess the available evidence for mystical-type experiences under psychedelics associating with medium-to-long term improvements in well-being or mental health, on their own and as compared with other features of the acute experience. Methods: I conducted a pre-registered, comprehensive review of existing empirical studies on the topic, based on a systematic search of the literature. Results: Forty-four eligible studies were found, with most reporting positive associations between mystical-type experiences and improvements in well-being or mental health. The current level of evidence appeared stronger among healthy people, in cross-sectional studies, and for links with positive changes in general well-being and life satisfaction, attitudes and behavior, and anxiety, than for depression or other aspects of well-being and mental health. A few studies suggested that psychological insights and emotional breakthroughs may be as or more closely associated with positive changes than mystical-type experiences. Conclusions: Despite their significant limitations, the identified studies suggest that mystical-type experiences under psychedelics are associated with improvements in some areas of well-being. However, psychological insights and emotional breakthroughs might be at least as important and should also be measured in future studies.