A naturopathic doctor told me this. I asked for the evidence, but they didn't have it on hand and were too busy. Let me note that I don't think this person is anti-maijuana. I asked them how they felt about its use and they just kinda smirked and said out of all the drgs it's the least harmful and that they don't just go and reccomend someone stops using it if they can incorporate it into their daily lives.