When people talk about illegal weed, the first thing that comes to mind isn’t actually marijuana. Its comfrey. Comfrey is a herb known for healing bones and deep tissue injuries, but it is presently listed as a noxious or illegal plant in Alberta.
Chamomile, which is used for skin irritations, is as well. So are poppies, shepherd’s purse, yarrow, and many other useful herbs and plants which are beneficial to butterflies and other pollinators.
The Codex Alimentarius which is a list held by several international governing bodies, dictates what is acceptable as food and what is not. I am not familiar with the guidelines of the modern codex alimentarius, but I am familiar with the fact that the older pre-United Nations one stated that garlic was not food but medicinal because eating it prevented illness, and therefore should not be made available through a grocer but via an alchemist.
Many of the herbs and plants that I consider essential to a basic medicine cabinet are considered illegal, noxious, or invasive (or all of the above) because of our modern insistence on factory farming. True, there are reasons for this with some of them – yarrow for example has the capacity to shoot taproots eight hectares from the main plant – but if reasonable prudent caution is exercised, there should be no real difficulty.
One of the main reasons for the Codex Alimentarius is to distinguish between food and medicine. And since almost everything you ingest has some sort of effect on your cells, for all intents and purposes, everything you eat is medicine.. this is the list that controls everything from additives to food hygiene.