This study is an interdisciplinary research into Uruguayan ayahuasca users belonging to one neo-shamanic and one Santo Daime group. The study involved the chemical analysis of ayahuasca samples, an ethnographic description of the two traditions and rituals, and the application of psychometric scales to measure personality di"erences, and the acute psychological e"ects during an ayahuasca ritual. Personality measurements showed lower scores for Santo Daime in Neuroticism-Anxiety, Dependence, Low Self-Esteem, Anger and Restlessness. These di"erences may be related to the presence of participants under treatment in the neo-shamanic group and/or to the protective e"ects of a church religion such as Santo Daime.