This is for new foragers, like my coworker:
'Medicinal' does NOT mean 'good for you and safe to eat all the time'. A plant being 'medicinal' does NOT mean that eating it, without any idea of WHY and HOW it's considered medicinal, is a good idea. It is UNWISE to consume a plant that has a long history of use in a way that DOES NOT have a long history of use.
In addition to learning that a plant is edible, you need to learn how it is eaten, what part is eaten, when it's harvested, and how to harvest it sustainably and in a way that supports its continued existence (unless it's invasive). If people only eat the ripe berries as food, then don't eat unripe berries. Don't. Eat. Unripe. Berries. UNLESS! There's! precedent! For that plant!
I know there's this idea going around that Americans only eat sweet or salty things, and that we've eliminated bitter things from our diet, and we should thus be eating more bitter things. But! Bitter things are bitter for a reason, and sometimes that reason is poison! Some of them are medicinally useful at the correct dose, but! You need to know what that is! You need to be doing it on purpose! DO NOT! Assume that bitter means that it's good for you!
Yes! Foxgloves can be medicinal in the right dose but they're also really poisonous if you just eat them randomly. Willow bark has the compound that can be refined into aspirin but if you eat it it's really easy to give yourself ulcers. Also, you must get a foraging book that is specific to your local environment, poisonous lookalikes vary by region
Eliminated bitter things from our diets? Nonsense, what about coffee?
Anyways, yes. Medicinal plants are medicines. They have drug interactions and side effects. You can overdose. Modern pharmaceuticals are a good thing because you know exactly how much of the active ingredient you are consuming, and there is a lot of information on the safety.
Also, like any food, you can randomly have a sensitivity or an allergy to a plant you haven't eaten before, so maybe only eat a little the first time you eat it.
OP, can I ask about your coworker. did something happen?
Yeah, he wouldn't stop eating unripe oregon grape (Mahonia nervosa, not at all related to actual grapes) berries, despite him being new to this area, new to the plant, new to foraging, and having multiple local experienced foragers telling him to stop eating unripe berries. Because he had heard that oregon grape was medicinal and translated that to 'good for you'. And that he was "pretty good at making" himself "eat things when they're good for you even if they taste bad". That is not a good attitude to bring to foraging plants that are new to you. And when I expressed concern that he was eating unripe berries that have no history of being consumed while unripe that I could find, he claimed that he'd seem it in two articles.
Turns out he was mixing up 'uncooked' and 'unripe'. What finally got him to stop was his concern for his microbiome, when I pointed out that part of how oregon grape is medicinal is as an antimicrobial. And unripe berries are sometimes not edible even when they're edible when ripe. And sometimes that's because they have more of the bioactive compounds than ripe fruit.
He luckily only had mild stomach discomfort. But you really, really shouldn't eat things in a way that no one else does.
This is also the guy who said "strawberry!" and popped an unripe black blackberry into his mouth before I could point out that it was an unripe blackberry. And miss identified a barberry as a rose. He's been very lucky so far, but that level of carelessness is extremely risky in foraging. I am trying very hard to get him to actually look at the plants he wants to eat and learn how people eat them.
