The following is the Bureau of Alcohol Tobacco Firearms and Explosives view on Marijuana use, regardless of the state you live in.
Please read this very carefully as it applies to all Marijuana users.
Please note: In case you think you might get around the federal law by answering "no" on the 4473, please note that knowingly falsifying a federal form has the following consequences:
Lying on a Federal Form (United States Code 18 Section 1001)
Under U.S. Code 18 Section 1001, it is illegal to knowingly and willfully make any materially false, fictitious or fraudulent statement or representation in any matter within the jurisdiction of the executive, legislative or judicial branch of the United States. A conviction for lying on a federal form is punishable by five to eight years in federal prison.
also note, that you can still face the consequences even if your background check (in CA's case, the DROS) is denied.
IMPORTANT NOTICE: Federal Law on Marijuana and Gun Ownership
This notice serves as a reminder to California Firearms Dealers (CFDs) that any person who uses, or is addicted to, marijuana is prohibited by Federal law from possessing firearms and/or ammunition regardless of current state legislation authorizing the legal use of marijuana for medicinal or recreational purposes.
With the passage of Proposition 64 on November 9, 2016, adults 21 years of age or older may now legally grow, possess, and use marijuana for non-medical purposes with certain restrictions.
Per the Bureau of Alcohol, Tobacco, Firearms and Explosives’ (ATF) Open Letter addressed to All Federal Firearms Licensees in 2011:
Any person who uses or is addicted to marijuana, regardless of whether his or her State has passed legislation authorizing marijuana use for medicinal purposes, is an unlawful user of or addicted to a controlled substance, and is prohibited by Federal law from possessing firearms or ammunition. Such persons should answer "yes" to question 11.e. on ATF Form 4473 (August 2008), Firearms Transaction Record, and you may not transfer firearms or ammunition to them. Further, if you are aware that the potential transferee is in possession of a card authorizing the possession and use of marijuana under State law, then you have "reasonable cause to believe" that the person is an unlawful user of a controlled substance. As such, you may not transfer firearms or ammunition to the person, even if the person answered "no'' to question 11.e. on ATF Form 4473. (https://www.atf.gov/file/60211/download)
Federal law [18 U.S.C. § 922(d)(3)] makes it unlawful for any person to sell or otherwise dispose of any firearm or ammunition to any person knowing or having reasonable cause to believe that such person is an unlawful user of, or addicted to, a controlled substance.
In a recent court case, Wilson v Lynch, the United States Court of Appeals for the Ninth Circuit held that the federal law prohibits registered medical marijuana users from legally purchasing firearms and/or ammunition. The Ninth Circuit unanimously agreed that marijuana and other drug use “raises the risk of irrational or unpredictable behavior with which gun use should not be associated.”
Further, CFDs are to expect a revised version of the ATF Form 4473 that will go into circulation on January 16, 2017, which will include the following new language:
"Warning: The use or possession of marijuana remains unlawful under Federal law regardless of whether it has been legalized or decriminalized for medicinal or recreational purposes in the state where you reside."
Should you have any questions, please contact the Bureau of Firearms, Customer Support Center at (855) 365-3767 or via e-mail at: email@example.com.