That means your plant production might reasonably be 60 to 100mg per day, or over a grow cycle of 100 days, that is 10,000mg. Some conditions like cancer, require much more, like 1000 mg per day for the better part of a month. This means that over a grow cycle, that is 30 g!! per month. However, that represents pretty much the maximum in the literature, and without a legitimate medical source, it's probably not going to go so well for you.
So, an average person can justify 100mg THC per day, and 10 grams over a 3 month grow cycle. If your weed is 20% THC, one ounce has 5000 mg THC in it. That means you can consume 2 ounces per month at 100mg per day, or 6 ounces over 3 months, which is something like a typical grow cycle. If your plants yield an ounce each, then six plants will do. If your medical use requires 400mg per day, that's obviously got to be for a serious condition, and the allowance will be 24 plants, that have a yield of one ounce.
At the end of the day, if you're really growing just for yourself, and maybe entertaining - giving away a bit here and there, and you have a recommendation, it's very unlikely there will be an issue, and if there is, there's ample scientific evidence to back up your medical claim, that is if you're following legitimate medical protocol.