With the recent changes in Maryland law concerning medical marijuana, see MD Code, Health - General, § 13-3304 et seq., and the push to legalize the use of marijuana in Maryland, a recurring issue is how such marijuana use would affect your Second Amendment rights. The short answer is that it may well act to abrogate those rights by (1) barring a FFL from selling a firearm to such a user and (2), by making such a user a prohibited person under federal law.
1. As to FFLs, the pertinent statutory provision under federal law is 18 U.S.C. 922(d)(3), which provides:
(d) It shall be 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--
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(3) is an unlawful user of or addicted to any controlled substance (as defined in section 102 of the Controlled Substances Act (21 U.S.C. 802));
The ATF has issued a bulletin to all Federal Firearms Licensees that advises FFLs that "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." See Open Letter to All Federal Firearms Licensees, Sept. 21, 2011, available at www.atf.gov/file/60211/download. That means that the FFL (or any other person with such knowledge) is prohibited from selling a firearm to such a person with a medical marijuana card. Indeed, both federal form 4473 and state form 77R specifically state that medical marijuana users may not purchase firearms.
2. As to becoming a disqualified person, a user of marijuana may well be a disqualified person under 18 U.S.C. 922(g)(3) which states:
(g) It shall be unlawful for any person--
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(3) who is an unlawful user of or addicted to any controlled substance (as defined in section 102 of the Controlled Substances Act (21 U.S.C. 802)); to ship or transport in interstate or foreign commerce, or possess in or affecting commerce, any firearm or ammunition; or to receive any firearm or ammunition which has been shipped or transported in interstate or foreign commerce.
A violation of these provisions is a felony. See 18 U.S.C. 924. Both of these provisions define the term "unlawful user" by reference to the Controlled Substances Act, a federal law. A "controlled substance" under federal law specifically includes marijuana as marijuana is specifically classified as a Schedule I controlled substance under the Controlled Substances Act, 21 U.S.C. § 812(c). See also ATF regulations 27 C.F.R. § 478.11. A user of marijuana is an unlawful user under that federal law. Period. Indeed, while the medical marijuana law of Maryland permits the use of marijuana under the tightly controlled circumstances specified in that law, the mere possession of marijuana in Maryland remains otherwise illegal in any other circumstance. See Robinson v. State, 451 Md. 94 (2017). That is so even though possession of small amounts of marijuana has also been decriminalized in Maryland. See Robinson, 451 Md. at 98 ("Simply put, decriminalization is not synonymous with legalization, and possession of marijuana remains unlawful.").
3. While the government does not have free rein in what it can illegalize under the Second Amendment (see, e.g., United States v. Chovan, 735 F.3d, 1127 (9th Cir. 2013) (Bea, J. concurring), these provisions have withstood attack in the courts. For example, the Ninth Circuit (a very liberal circuit) has sustained this federal disqualification in the context of medical marijuana users on grounds that "empirical data and legislative determinations support a strong link between drug use and violence. As to the first, studies and surveys relied on in similar cases suggest a significant link between drug use, including marijuana use, and violence. See United States v. Carter, 750 F.3d 462, 466–69 (4th Cir. 2014) (citing and discussing four studies and two government surveys); United States v. Yancey, 621 F.3d 681, 686 (7th Cir. 2010) (per curiam) (citing all but one of the studies and surveys in Carter, plus one additional study). " Wilson v. Lynch, 835 F.3d 1083, 1093 (9th Cir. 2016). The court concluded that Congress reached a "reasonable conclusion that the use of such drugs [including marijuana] raises the risk of irrational or unpredictable behavior with which gun use should not be associated." Id at 1094. It is certainly within the power of Congress to change federal law, but until it does, marijuana users remain "unlawful users" of a controlled substance under federal law, regardless of whether such use is permitted by state law. Of course, the states would have to change their laws as well, as the classification of "unlawful user" includes both federal and state laws.