• The recreational use of plants for their stimulant, aphrodisiac, or hallucinogenic effects is ancient, and throughout the ages plants have been used as poisons. • Many plants that are regarded as poisonous have been used for their supposed therapeutic properties, but while many can still be found in herbals, not all have found their way into modern formularies. In contrast, many tropical plants are used herbally, although evidence of efficacy is often poor or lacking. • Traditional medicines exist in many forms and lack standardization; very few have been rigorously tested for toxicity, especially for their long-term effects. • Traditional medicines are often prescribed as complex mixtures with uncertain pharmacology, or are prepared and taken by patients themselves. Poisoning occurs because the herb is itself toxic, has been mistaken for another plant, mislabelled, mixed accidentally or deliberately with other, poisonous, plants and medicines, contaminated with insecticides or herbicides, or, as in the Asian kushtays, mixed with appreciable amounts of heavy metals. Herbal medicines are also used in combination with allopathic drugs, and the often unpredictable effects of such combinations add to the hazards. • Plant poisoning can occur as a result of accidental, unknowing, or deliberate poisoning from contaminated foodstuffs or from toxic seeds and fruits; from the misuse of traditional or herbal medicines; or from the deliberate use of plants for their psychotropic or supposedly aphrodisiac properties.