In "Early Medieval Balkans" by John Fine Jr, he reports that Bajan, the fourth son of Bulgarian Emperor Symeon, was reported by one source to have studied magic and possessed the power to transform himself suddenly into a wolf. The author goes on to coyly write, "Whether Bajan... achieved his transformations, as our source states, through magic practices, possibly through hallucinogens (a means which can be documented for seventeenth-century European werewolves), is unknown."
Could someone please elaborate on whatever 17th-century documentation of werewolves he's mentioning???
Probably referring to Jean de Nynauld's De la lycanthropie, transformation et extase des sorciers (1615) or possibly Jean Bodin's De la démonomanie des sorciers (1580), although that's really a bit too early. Both contain accounts of lycanthropy and witchcraft connected with the use of magical ointments, whose components include herbal hallucinogens. In The White Devil: The Werewolf in European Culture author Matthew Beresford quotes (a translation of) de Nynauld in giving the ingredients for the lycanthropic ointment as:
belladonna root, nightshade, the blood of bats and hoopoes, aconite, celery, soporific nightshade, soot, cinquefoil, calamus, parsley, poplar leaves, opium, henbane, hemlock, varieties of poppy and crustaceans.
Many of which are outright poisonous to varying degrees, and a few of which are hallucinogens or psychoactive in the right quantity/potency.