I thinks there's something to the use of marijuana to deal with the pain of cancer. While marijuana is not an analgesic itself, it is anxiolytic, which can help ease the psychological stress of pain. There are some articles out there about THC receptors not only being present in the central nervous system, but also on white blood cells, where they *may* modulate immune function.
But, at this point in time, I just don't see any legitimate gastroenterologist urging their patient to smoke marijuana, especially when they know it's going to lead to an automatic suspension. A good doctor would search for appropriate alternatives. Although different, smoking tobacco can really worsen a patient's Crohn's. While marijuana is not tobacco, the point is smoking marijuana could even be harmful for Crohn's, we just don't know and need much more data before labeling it "beneficial".