Tea at Trianon links to an article on British Herbal books in medieval times
herbal medicine in the past was a skill, and if some old ladies were accused of witchcraft, it might be because people died from the herbs...not only accidental overdoses, but from abortion causing herbs or because someone wanted to "off" an elderly parent or inconvenient spouse.
The Inquisition, ironically, was instituted partly to stop lynch mobs against the accused: They would actually investigate and often say the accusation was wrong. Most of the inquisition's black legend is that: Propaganda, greatly exaggerated by those who hated Catholics.
But herbs are dangerous.
most work by "placebo effect", but those that do have active ingredients often have a close "theraputic/toxic" ratio: meaning if you give enough to work you might be close to killing the patient.
For example, when I started medical school, we still used digitalis extract, which could vary in strength from batch to batch, depending if the leaf was grown in the sun or in the shade (e.g. cloudy days). Then they came out with Lanoxin (digoxin). The brand name was from the plant grown in central Canada by irrigation, so the variation was minimal.
But we still didn't have a way of testing the drug level, so digitalis related overdoses was still a major cause of death and hospitalization.
When someone was in congestive heart failure, we loaded them up, essentially using the criteria first described in 1790: give doses until they either pee (diuresis), vomit, or get diarrhea (signs of overdose). We also could check the EKG for heart block, and another sign of toxicity was vision that saw yellow halos around lights etc.
Then came lasix, the ACE blockers, etc and we pretty well stopped using it, except maybe to slow the heart down in atrial fibrillation. Too dangerous.
I suspect similar problem with other herbs.
And in Africa, often accidental herbal poisoning was a cause of death. We had outreaches with the local N'angas (aka "witchdoctors"). One was to encourage them to refer to us if the bewitched person who was losing weight didn't get better, to check for TB. Another was to encourage quality control in their dosages (i.e. care in concocting the medicines by proper measuring etc).
When I hear about "mind body" medicine, I shrug because a lot of this is hypnosis/suggestion/placebo effect. And indeed, one Nigerian psychiatrist I dated in Liberia was the grandson of an herbalist/witchdoctor, who told me the story that during the Nigerian cisvil war, when they ran out of anesthesia, he would hypnotize them as his grandmother taught him to do, to control the pain.
There is a reason for scientific medicine: Herbs do work, but like the Reiki and other mind body things, a lot is hypnosis, and a lot is the magical idea that you are in control of your life, so can heal yourself.... heal as in "I am in control (when you are sick, you are vulnerable because you aren't in control, hence religion)... and of course, you do it yourself, meaning no expert needed (feminist who hate men doctors are especially prone to do this... even now, with women docs, the feeling is the same because the dirty little secret is that these men haters really hate doctors of either sex because we studied 8 to 12 years and know more then they do and they are jealous.)
I had quite a few herbal books (some I brought with me here). And you know what? They don't agree with each other
and a lot of those that work are in a book I have is a field guide about "dangerous plants" in the eastern USA...many of these plants are now weeds, brought by early settlers, and I often found them walking through the woods and glades outside our coal town (where farms had been abandoned a century earlier, when the mines opened, but the mints, blackberries, elder berries, apple trees etc. still were there).
Related book: Wicked plants.