18 USC 922 (g) – Federally Prohibited Persons
The Federal Gun Control Act of 1968 and the Federal Omnibus Consolidated Appropriations Act of 1997 make it illegal for a person who fits into any of the following categories to ship, transport, receive or possess firearms or ammunition. These laws prevent a state from issuing a concealed carry license/permit as it would be illegal for people who fit in these categories, by federal law, to own or possess a gun.
18 USC 921 (a)(33)(B) – Exceptions
(ii) A person shall not be considered to have been convicted of such an offense for purposes of this chapter if the conviction has been expunged or set aside, or is an offense for which the person has been pardoned or has had civil rights restored (if the law of the applicable jurisdiction provides for the loss of civil rights under such an offense) unless the pardon, expungement or restoration of civil rights expressly provides that the person may not ship, transport, possess or receive firearms.
Federal law prohibits medical marijuana users from possessing or buying firearms and ammunition — even if state law allows the drug’s use. An individual can’t have both licenses. Under federal law, any marijuana user is an unlawful user of a controlled substance. The 9th Circuit Court of Appeals has upheld this rule. Marijuana in any form is illegal under federal law. Users of marijuana are prohibited persons. Checking ‘no’ on question 11(e) on the Form 4473 would be a lie if you use marijuana. See this ATF letter on the topic.