Background: Diets combine food types according to some trade-offs, as for example maximising nutrients and minimising toxins. But some diets include elements because of their activity against the host parasites and other pathogens. This so-called medicinal role of food is under-reported in the literature, either because toxic elements in diets of livestock and wildlife are infrequent, or because their activity against parasites and pathogens has not been fully documented. We contribute to fill this knowledge gap by testing the activity of extracts and essential oils from Papaver rhoeas and Echium plantagineum against a selection of laboratory pathogens. These plants are strongly selected by great bustards Otis tarda during the mating season. Results: During this season we found a significantly higher frequency of P. rhoeas in male than in female faeces. The activity of different extracts of these plants against some laboratory models including a flagellated protozoan (Trichomonas gallinae), a nematode (Meloidogyne javanica) and a fungus (Aspergillus niger) was evaluated. We found activity against nematodes and trichomonads in non-polar and polar extracts of the aerial parts of P. rhoeas, especially the extracts of flowers and capsules, and E. plantagineum, especially the extracts of leaves and flowers.Conclusions: Both plants showed anti-parasitic activity, a result compatible with the hypothesis that great bustards eat plants for non-nutritional purposes, likely to assist them in coping with parasites and other pathogens, and P. rhoeas could be especially helpful for males during the mating season, when their immune system is weakened by the investment in secondary sexual characters and sexual display. The self-medication properties of plants and animals included in diets should be considered in studies of foraging behaviour, habitat selection, and even conservation biology of wildlife.