The Hindu deity Dhanvantari stands as the god associated with Ayurveda, described as an avatar of Vishnu who brought medical knowledge to humanity. Some texts frame the work as teachings delivered by King Divodasa of Varanasi, who was considered an incarnation of Dhanvantari.
Ayurvedic treatises describe three elemental doshas known as vata, pitta, and kapha. Vata represents air while pitta signifies bile or fire and kapha denotes phlegm or earth and water.
Historical research dates the compilation of the Sushruta Samhita to a period starting from the first century BCE and revised into its present form by about 500 CE. The Charaka Samhita is also dated to between the second and fifth centuries CE in its current form.
Critics assert that these doshas are not real but rather a fictional concept lacking scientific basis. A random sample study found that twenty percent of rasa medicines sold on the Internet in 2005 included toxic heavy metals like lead, mercury, and arsenic.
Between 1978 and 2008 more than eighty cases of lead poisoning associated with Ayurvedic medicine use were reported worldwide. The U.S. Centers for Disease Control and Prevention linked Ayurvedic drugs to lead poisoning based on cases where toxic materials were found in the blood of pregnant women who had taken these remedies.