Datura metel
A member of the Solanaceae certainly suggests itself as a suitable candidate, but through lack of any physical description of the plant the quoted passages can at best only suggest the identification of "da dhu ra" as Datura metel on the basis of toxic effects common to other indian Solanaceae. Nonetheless, the "Vajra-mahabhairava-tantra" occurrences at least provide a roughly datable (and definitely pre-Columbian) record of the word "da dhu ra" on the basis of which the linguistic evidence can be investigated.