Cannabis has properties similar to other illicit drugs but it's lasting influence on the body is good medicine I think, and so does modern research.

Cannabis restricts oxygen to the brain? How much oxygen does the brain need to operate nominally? What percentage of oxygen is reduced when cannabis is consumed? Does this also include vaporized or oral cannabis? Does the alleged limitation of oxygen actually cause damage? Get back to us when there are answers.

It is irresponsible to list negative (or positive!) effects of cannabis without providing some sort of background. Withholding scientific information only contributes to the propaganda effect.