Here are a few links about mj as a treatment for asthma. Believe what you want, but I would encourage you not to accept college textbooks as much of an authority on anything. Sometimes they make reference to a real authority like a professional journal article or published study, but the much of any textbook's content is motivated by the publisher's profits. Books have to be politically correct, not offend anyone, and not question the law or government. Often the Feds actually pay media publishers to include the anti-drug propaganda in the content of the book. They do this with TV shows, too, if sitcom writers create an episode where little Johnny learns that drugs are bad, m'kay?, then they get money from the Feds.
http://www.druglibrary.org/Schaffer/hemp/medical/tashkin/tashkin1.htm
http://www.showmethefacts.org/medical-marijuana-facts/asthma/
http://answers.yahoo.com/question/index?qid=20061025201839AAsuN48
It didn't until the Civil War. Now it does. States' rights today is an academic concept only. States only have rights when the Federal government approves. Otherwise, the "United" States would be a voluntary association, a confederacy, which was what the south was fighting for. We like to think that the war was fought over slavery, because it makes it seem like the good guys won.
The Feds bust med mj users and distributors in California all the time. Mostly what they do these days is bust in the door of a dispensary, flash guns, and steal all the cash. Then they run like the thieves they are. It's about impossible to get seized money back from the Feds. You have to pay a lawyer $25 grand and then your odds of winning are still horrible. The legal standard is basically proving your own innocence. If criminal trials were that way, we would have more prisoners than citizens. So the owners of the dispensaries spend their time collecting duffel bags of cash from their stores and hiding it before the Feds or the gangs can rob them. All of this is because the Feds won the Civil War.