I'd like to offer a personal opinion regarding this. Marijuana CAN be medicine, just like Morphine CAN be medicine. Both can also be intoxicants. It's all about the intent
of one's usage. If you are using Morphine to treat severe pain, and not using it to get high, then it is not a violation of the 5th. precept. If, OTOH, you are using it to get high, you are using it as an intoxicant and it most assuredly is a violation of the 5th. precept. I don't think anyone disagrees with this point.
In a similar light, if Marijuana is being used to treat a medical condition and not to get high, then you're not in violation. If you're using it to get high, you're in violation of the 5th. precept. I don't see what can be more clear.
It's all about INTENT.
Now, anyone who has used Marijuana and hasn't gotten intoxicated, I respectfully submit to that person that you have not been smoking very high quality bud
I have some small experience in this matter. In fact, I have quit using Marijuana because of the 5th. precept. Again, please note, I was using it to get high, not to treat a medical condition, though I technically was able to obtain it semi-legally (I say semi-legally because no where in the United States with a VERY few exceptions, is Marijuana legal under FEDERAL law.) I do know some people who use Marijuana to treat legitimate medical conditions and a subset of this group is VERY careful about using only enough to treat their condition and not to get high. I'm confident enough in the way they use it to say that if they were Buddhists (they are not) that they would not be in violation of the 5th. precept.
I do know that the human capacity to fool oneself is nearly infinite, so I could lie to myself and say that Marijuana doesn't get me high, I only used it to treat social anxiety, help me sleep and relieve the general aches and pains that most 52 year old's generally experience out of having lived for 52 years! But I would be lying to myself. I used Marijuana to get high. That's why I quit. I do not want to violate the 5th precept. Now, was this easy? Actually, it wasn't hard at all for me to quit because the improvement in my meditation has been absolutely remarkable. I can't speak for anyone else, but Marijuana "messes" with my meditation because it gave me a false sense that I was actually improving in my meditation in a way that I wasn't, naturally. I did experience some mild withdrawals, but nothing that serious. Probably somewhere between quitting coffee and quitting cigarettes. CERTAINLY not to the level of quitting opiates.
Now, to the OP's original question. Having frequented a fair number of SoCal's finest dispensaries, in San Diego, Orange and LA counties, I can count on one hand, nay, one FINGER, the number of shops that were oriented toward the truly ill and not simply fun places to buy pot to get high.
Everyone has to make their own decisions on these things, but I think that anyone who is foolish enough to claim that Marijuana isn't an intoxicant is either smoking really low-grade weed...or is fooling themselves.