Zoopharmacognosy is a behaviour in which non-human animals apparently self-medicate by selecting and ingesting or topically applying plants, soils, insects, and psychoactive drugs to prevent or reduce the harmful effects of pathogens and toxins.[1][2] The term derives from Greek roots zoo ("animal"), pharmacon ("drug, medicine"), and gnosy ("knowing").

An example of zoopharmacognosy occurs when dogs eat grass to induce vomiting. However, the behaviour is more diverse than this. Animals ingest or apply non-foods such as clay, charcoal and even toxic plants and invertebrates, apparently to prevent parasitic infestation or poisoning.[3]

Whether animals truly self-medicate remains a somewhat controversial subject because early evidence is mostly circumstantial or anecdotal,[4] however, more recent examinations have adopted an experimental, hypothesis-driven approach.

The methods by which animals self-medicate vary, but can be classified according to function as prophylactic (preventative, before infection or poisoning) or therapeutic (after infection, to combat the pathogen or poisoning).[4] The behaviour is believed to have widespread adaptive significance.[5]

In an interview with Neil Campbell, Rodriguez describes the importance of monarch butterflies preferentially lay their eggs on toxic plants such as milkweed which reduce parasite growth and disease in their offspring caterpillars.[49] This has been termed transgenerational therapeutic medication.[50]

When fruit flies detect the presence of parasitoid wasps, they preferentially lay their eggs in high-ethanol food; this reduces infection risk in their offspring.[50] This has been termed transgenerational prophylaxis.[50]

In an interview with Neil Campbell, Rodriguez describes the importance of biodiversity to medicine:

"Some of the compounds we've identified by zoopharmacognosy kill parasitic worms, and some of these chemicals may be useful against tumors. There is no question that the templates for most drugs are in the natural world."[21]