Self-medication in nonhuman primates: A systematic evaluation of the possible function of the use of medicinal plants

Animal self-medication is thought to provide an adaptive advantage, as species would actively respond to a disease state or homeostatic imbalances. In wild nonhuman primates, it is challenging to differentiate plant use as part of the diet or as medication, especially because self-medication can be preventive or therapeutic. Here, we aimed to compile the available potential evidence on primate self-medication modes, investigating which proposed requirements are fulfilled for each plant species reported to date. We systematically reviewed the scientific literature on plant use for potential self-medication in wild nonhuman primates. To construct the extensive database, we extracted data on the primate species, study area, plant/plant's part used, the requirement(s) met for demonstrating self-medication modes, and self-medicative behavioral patterns. We also updated available information on plant's biological compounds and/or physical characteristics, pharmacological properties, and ethnomedical uses. We identified 575 plant species (135 families), used by 25 primate species (9 families). Plants were used by Old World monkeys (46.5%, n = 268 plant species), followed by apes (41%, n = 235), New World monkeys (13.4%, n = 77), and prosimians (1%, n = 6). We found three general types of self-medicative behaviors: ingestion (including, but not limited to, leaf-swallowing, seed-swallowing, and bitter pith chewing), topical (fur-rubbing), and nest fumigation. Plant uses were associated with antiparasitic, antibacterial, antimalarial, anti-inflammatory, insect repellent, among other properties. Self-medication is widespread in nonhuman primate species across Central and South America, Africa, Madagascar, and Asia. Long-term field research efforts and studies integrating different research sites and topics are urgent to advance our knowledge into the evolution of plant selection, medical traditions, and to bring insights into potentially novel medicinal plants and bioactive compounds to treat emergent or established primate and human diseases.