In this review I examine the clinical uses of psychedelics as an adjunct to psychotherapy to treat three major mental health disorders; Major Depressive Disorder (MDD), Post Traumatic Stress Disorder (PTSD) and Addiction (Substance Use Disorder). I assess the hallucinogen treatment model's efficacy in treating chronic mental health disorders that have been unresponsive to legal and traditional psychiatric treatment. I review the earlier studies conducted with psychedelics and discuss the more recent ones. This review may be helpful to therapists and clinicians who would like to further their understanding of psychedelic therapy.