[vorpalhex]

Except those alternatives will kill you dead if mishandled.

This isn't a choice between "cough medicine" and "slightly less effective cough medicine", it's a choice between a controlled and inspected product and random plants that may or may not be the right genus, dose and concentration.

[blacksmith_tb]

'Wrong Genus' seems to be giving monks and other gardeners less credit than they deserve? Sure, amateurs foraging for wild herbs could make some dangerous mistakes, but if you're intentionally growing a plant it's presumably the right one?

[vorpalhex]

Frequently it's not. Seeds can be mislabeled and many plants are extremely difficult to identify reliably, much less grow to have a consistent dose of whatever active ingrediant.