Colorado Campaign for Equal Gun Rights
In Colorado, a group is working to add this language to Colorado laws via a ballot initiative:
"
18-12-203. Criteria for obtaining a permit. (1) Beginning May 17, 2003, except as otherwise provided in this section, a sheriff shall issue a permit to carry a concealed handgun to an applicant who:
(c) Is not ineligible to possess a firearm pursuant to section 18-12-108; or federal law;
(f) Is not an unlawful user of or addicted to a controlled substance as defined in section 18-18-102 (5), EXCEPT THAT A SHERIFF SHALL NOT USE A PERMIT APPLICANT’S LAWFUL USE OF MARIJUANA PURSUANT TO SECTION 14 OR 16 OF ARTICLE XVIII OF THE STATE CONSTITUTION AS A BASIS FOR DENYING THE APPLICANT A PERMIT. Whether an applicant is an unlawful user of or addicted to a controlled substance shall be determined as provided in federal STATE law and regulations"
http://coequalgunrights.org/
There are two types of legal marijuana use in Colorado -- medical marijuana which is issued pursuant to a doctor's prescription and recreational marijuana which merely requires the purchaser to prove they are resident of Colorado.
In theory, the database containing the medical marijuana cards are medical records and cannot be obtained by anyone (but that's not been tested with a subpoena). The business records of recreational outlets are just non-confidential business records, so if the Department of Revenue or the CBI or local law enforcement demanded them, they would likely be turned over. There are hundreds of thousands of marijuana Rx's in Colorado, so the overlap with gun ownership must be significant.
If you've not seen it, Wayne LaPierre's column this month cites to an interesting case -- Haynes v United States -- where the defendant did not register a short barreled shotgun because registration would violate his 5th Amendment right against self incrimination. If you believe that case is binding, then one could argue that any declaration by a marijuana user on a CHP application could be deemed to violate the 5th Amendment's right against self incrimination and the applicant could refuse to answer. Whether a refusal to answer would result in a denial is an open question. Here's the link to LaPierre's column. It's worth reading.
http://www.nrapublications.org/index.php/19328/standing-guard-59/
If you want to keep your firearms, I suggest that you do not get a marijuana Rx or visit a recreational outlet. Eventually, the anti-gun administration will weigh the political consequences of fighting legalized marijuana against criminalizing gun ownership and, unfortunately, gun owners will draw the short straw.