Presently, C. sativa has four medicinal values. First, it is used to relieve nausea and increase appetite. Second, it brings about the reduction of intraocular pressure in glaucoma. Third, it causes a reduction of muscle spasms. Fourth, it provides relief from mild to moderate chronic pain (Anon., 1996a).
POST EDIT: #1 is particularly important for chemotherapy patients...where it is frequently recommended by doctors.
oh...and...
In a study in 1982, researchers analyzed the biological effects of chronic use of marijuana in human subjects. Pathological and biochemical tests were in a normal range. Chronic use did not produce serious, harmful effects in humans and a general medical examination showed no abnormalities. The researchers also concluded that marijuana can act as a hypotensive and reduce blood sugar, which is useful for treating hypertension, especially diabetic hypertension (Singh et al., 1981).
Face it folks, you are dealing with someone who has an irrational belief structure surrounding cannabis sativa...a naturally occuring substance that humans have been enjoying for thousands of years.
It seems to be based on actual circumstances, making it all the more difficult for him to do anything but remain rigid in his beliefs.
The fact that the rest of us know or have known human beings that did not turn into stupified, laid back, long haired hippie freaks with an IQ somewhere between a shoe size and Ozzie the first time they sparked a doobie will be quite lost on him.
Give up already.