For pain management and quality of life, we probably don't need to worry about the placebo effect too much; instead, we should just measure whether cannabis gets people off opiates.
This is something that could be major. My wife was in the hospital off and on this summer with stomach pains. The doctors couldn't figure out what was wrong (ran all of the tests, put her on liquid diet and the pain continued) so her doctor put her on OxyContin until the HMO approved a referral to a research university. The insurance declined the referral stating they wanted a second opinion, so my wife went to get one and the doctor wanted her to get off all of the medications. She did and almost killed herself the day after; the withdrawal from the OxyContin was terrible. If there was a way to manager her pain without constantly worrying about her becoming addicted or worrying that when she stops the med she will end up doing something drastic, it would be amazing!