In a recent study, Hardy et al. (2012) identified compounds from two non-nutritional plants, yarrow and camomile, in a sample of Neanderthal dental calculus from the northern Spanish site of El Sidrón. Both these plants are bitter tasting and have little nutritional value but are well known for their medicinal qualities. Bitter taste can signal poison. We know that the bitter taste perception gene TAS2R38 was present among the Neanderthals of El Sidrón (Lalueza-Fox et al. 2009), and their selection of yarrow and camomile was hence probably deliberate. With few nutritional benefits, reasons must be sought for why the Neanderthals collected and ingested these plants. They could have consumed them as flavouring, but this presupposes a degree of complexity in cuisine for which there is little evidence. The widespread evidence for animal self-medication, or zoopharmacognosy, however, offers an attractive behavioural context.We propose, indeed, that these plants were selected and ingested deliberately for the purpose of self-medication.Here, we investigate the implications of this new finding for Neanderthal knowledge of plants and we offer a context for plant knowledge and self-medication among early human and hominin populations.