I was talking to someone the other day who seemed vaguely rational. A family member was present having had a troubled year or two and wanted a ride to buy something. Naturally I was concerned and voiced my unease due to experience of previous drivers
“Do I look like I'm on the marihuana?” he said. It could have been anything really, toadstools, cactus juice, they all grow naturally after all.
“You don't look like that
NOW,” I replied.
When assessing visitors brought home by family members,
remember: they are fully capable of washing, tidying their hair, borrowing some clothes that aren't iridescent purple & orange zigzag spirals, even wearing shoes. The first impression could be just that and thorough questioning is appropriate. I believe "air fresheners" are available with Mary Jane infusions; perhaps one or two kept handy and undone during your interview would elicit a tell-tale response.
I hope this is helpful for concerned family members.