I work in a hospital and we use the drug "Marinol" all the time. As I understant it, it is a synthetic form of THC. We use it to increase appetites, in select patients. I'm not sure of its effectiveness compared to the real thing, but I have read that it is less effective.
They just don't want the general society to realize that they can get relief from a slew of ailments with a plant that nearly anyone could grow. Instead they make everyone rely on overpriced pharmaceuticals that frequently come with dangerous repercussions to the body.