Do hallucinogenic experiences determine cultural contents, or alternatively, does culture determine the contents of hallucinogenic experiences? Some authors have championed the neuropharmacological determinism thesis while others have endorsed the cultural determinism thesis. Both theses have important weaknesses: they are based on the study of a restricted number of ethnographic cases (anthropological comparativism is missing) and they are based on the study of a restricted number of hallucinogenic substances (neuropharmacological comparativism is missing). I will champion a third position: weak and plural neuropharmacological determinism. After having identified different classes of hallucinogens and pinpointed their mechanisms of action and their respective psychological effects, I examine the way rituals are distinctively shaped by neuropharmacological determinisms. Datura-based rituals (i. e., anticholinergic rituals) of North American are thus compared to ayahuasca-based rituals (i. e., serotoninergic rituals) of Amazonia, and subsequently compared to Jivaro rituals of the Montaña involving the use of both anticholinergic and serotoninergic hallucinogens. In conclusion, it is shown that far from being always competitive, cultural and neuropharmacological factors often prove synergetic.