Itís never technically altogether legal to fly on commercial airlines with weed because the airports all fall under federal jurisdiction, and marijuana is still illegal under federal law. However, TSA policy and anecdotal reports suggest that passengers who travel between states in which they can legally use pot are likely to be allowed to fly.
The reason is that although TSA reserves the right to ruin your day if they so choose, their official policy on drugs is to refer them to local law enforcement. So if the passenger has authorization to use medical marijuana, or if he or she is flying between Washington and Colorado, where possession of the drug even for recreational purposes has been legalized, local law enforcement isnít going to intervene.
According to a statement on the TSA web site:
TSA security officers do not search for marijuana or other drugs. In the event a substance that appears to be marijuana is observed during security screening, TSA will refer the matter to a law enforcement officer....