Where Is the Line between Food Plant and Medicinal Herb?

I noticed when I was pregnant that plants that I considered "food," like nettle and dandelions were considered "medicinal herbs," not to be consumed while pregnant. Meanwhile, things like soybeen (estrogenic effects) and cottonseed oil (lowers sperm counts) were considered fine to eat. Why are so many wild &/or perennial edibles (like sweet cicily) considered medical and "not safe to eat while pregnant or breastfeeding" but GMOs, fast food, and processed oils are safe? Are these wild &/or perennial veggies actual dangerous, or just unknown?

There is no line in the real world! In the legal world, many things that are safe are listed as not safe for pregnant or nursing mothers because they are not thoroughly tested.

I subscribe to the idea that food is medicine. I'm also very careful when pregnant, I keep things very simple and don't take much in the way of supplements or herbs. I dint even use most essential oils. I eat dandelion greens though!

That's actually what I did while pregnant, too, including eating dandelion. I had miscarried my first (only a month pregnant) and did not want to risk anything harming this baby. But, when people ask me (since I seem to be the resident "health nut"), if such and such is healthy to eat while pregnant, I just have no idea what to say, because the info is so varied an confusing. It also worries me, now, if "edible plants" are just "not-poisonous," if they have ill effects if eaten on a daily/weekly basis, etc. I just don't know enough!

Most whole foods are ok, some herbs and spices are questionable. Too much of anything is usually not good.

The simple answer, not much difference at all. Many foods are also medicinal (garlic for instance). The key distinction, as I understand it, is that food plants provide phytonutrients that are essential for building and repair needs in the body while herbs are focused on stimulating specific pathways in the body or other more specific targeted function. So garlic, for example, would have carbohydrates, vitamins, minerals, etc that are "food", but also has sulfer compounds that aid in detox pathways and antimicrobial functions.

Most of the warning labels on herbals are in the CYA (cover your ass) category and have very little basis in practical clinical application. For example, Kava was yanked off the American market about 12 years or so ago after two people had a serious reaction to the herb. Kava was finally allowed back on the market recently but has warning labels all over about possible liver damage. Turns out that the two confirmed cases both had a very rare preexisting genetic liver disorder that interected poorly with Kava. All the rest of the millions of users around the world can safely use with no problems. Compare this with a certain widely prescribed "cholesterol lowering" statin drug, which has a long list of side effects and has put a number of people on the liver transplant list.

Most of the biggest concerns with negative herbal reactions have to do more with overlapping function or interference with medications that the patient may be on. For example, asprin was originally derived as an isolate from white willow bark. Both have pain killing and blood thinning properties so taking both would result in too much blood thinning and thus be a problem. The typical medical doctor would therefore say don't take the white willow bark, since they would prescribe the asprin. I would rather they get off the asprin and take the safer option.