I don't know anybody who uses that as an excuse. I know people who have a legitimate medical use for pot, and I know people who enjoy it recreationally who are happy they can give the state some money in exchange for being legally allowed to grow/carry/smoke it, but I really don't know anyone who claims to need it for medicinal purposes when they obviously just want to get stoned for shits and giggles. Except for when they have to tell the state that, obviously.
