The federal government can deny you your Second Amendment rights if you use a controlled substance.
A holder of a duly authorized Washington state medical marijuana card in Richland, Washington applied for a Concealed Pistol Permit. According to the letter from the Richland police department, quoted by Bob,
federal law prohibits anyone who uses a controlled substance from “shipping, transporting, receiving or possessing firearms or ammunition.Whoops. Oh well, any excuse to keep people from owning guns, I guess. I wonder if President Obama will be in as much of a hurry to announce that his Justice Department won't be enforcing this rule as he was with the possession of marijuana laws that he has unilaterally thrown out.
I suspect that this will have a significant effect considering the previous story about marijuana dealers in Washington having to carry around large sums of cash since banks won't do business with them. Apparently the administration has issued guidelines about how the banks can do business with them, but would you trust the federal government if they said "It's illegal but we promise not to prosecute you"? I don't expect a lot of banks to take them up on their offer.