"Different types of cannabis have different ingredients,"
Actually strains could be developed that would have higher levels of tetrahydrocannabinols and then reduced to oils where the dosage could be controlled. It could then be put into foods that one would have as an evening snack.
Of course that could not have a patent so the pharmaceutical companies wouldn't be able to make money on it.
We do not know the long term side effects that marinol might have in healthy patients since it has been used primarily in patients with cancer on chemo and other more terminal type diseases.