I know many people who use Marijuana medicinally, both prescribed and not - my research has taught me that it is no more addictive than anything else you enjoy, and does little damage if any (It's certainly difficult to tell if it brought on any negative results) I think a lot more research needs to go in to how it "impairs" people who are use to it's effects as I've witnessed people do complicated math problems and delicate procedures under what I would consider heavy influence.
A few facts to consider:
Marijuana has never directly killed anyone (though there is a joke about someone dying by being crushed by it falling on them online somewhere) even heat stroke kills roughly 1 in a million Americans each year.
The leftovers and weak/diseased product has nearly unlimited uses, from clothing to bio-fuel (aka hemp which is the male plant).
The majority of medical marijuana users drop all other medications.
Many people believe "big pharma" wants to keep you sick, and their reasoning is logical.
I think the most convincing publications I've seen on its potential use is https://www.youtube.com/watch?v=zNT8Zo_sfwo
I myself have tried it and in small doses it's relaxing and will give restful sleep, munchies and perhaps a minor dizziness or tummy ache - In large doses it will remove nearly any care in the world (including sever pain) and likely make you to sleep in... unless maybe you have an allergy or something.
... at any rate It's unquestionably far superior to alcohol as a recreational substance.