I should have asked before. What kind of studies are you talking about? Are you talking about studies using smoked marijuana to relieve some condition?
Just how would that study be conducted? It wouldn't be all that scientific and it would probably be no better than anecdotal information.
C'mon. This isn't science.
What can't you conduct studies the same way you would for any other substance? Obviously a double-blind study would be difficult as the smell is so distinctive - it would be tough to find an inert placebo substance, though you might be able to find a group that honestly didn't know what the real stuff smelled like so they could be more easily fooled with a substitute. Still, there are ways of conducting a study just as with any pain-relieving drug: Visual analog scales, functional scales, and the like. Weight gain is also an objective finding - take any group of people on a specific chemo drug and have half of them smoke and see what the weight gain or loss is.
What sort of scientific background do you have, BTW?