There is not much literature regarding the possible effects and interactions of the pan-Amazonian hallucinogenic brew ayahuasca and cannabis, except for some anthropological research. One specific Brazilian religious group had used both substances as sacraments in the past, so here it is reported a brief theoretical scientific overview of the possible interactions and risks between those two substances in humans. The main risks were found to be associated with the possible occurrence of cardiac problems, anxiety and panic reactions, and also psychotic reactions. Nevertheless, some “positive” and neutral interactions are also commented.