In have a friend who has MS and uses medical cannabis although not when he is the US. Here in Israel the law is being relaxed. As of now it requires a special permit from the Ministry of Health and can only be prescribed by certain doctors and sold by certain pharmacies.
[the prescribing of marijuana]
However, I don’t understand why it needs a hechsher, especially in Chul where there is no issue of terumot and maaserot, as it is a medication and not just a food supplement like vitamins.