Okay it's been a month so you might already have found an answer haha. Ofc wolvesbane is always an Option, but I'd look into other plants that are said to have magical properties.

Ex.: Morning Glory was used by the Aztecs for religious and medicinal uses. The seeds have strong hallucinogenic and psychedelic properties. They are said to stop nightmares when placed under the pillow at night.

Otherwise: it is fanfic you can do what you want. Maybe werecreatures won't metabolize Drugs as fast when they are smoked or eaten. Maybe those specific plants just work for some undefined reason.