Do California Cannabis card holders forfeit the right to legally own a gun?

That is a debate making the rounds of the 2nd Amendment legal community. The federal and state laws provide that you are barred from possessing a firearm [or ammunition] as a prohibited person if you are an unlawful user of, or addicted to, marijuana, or any depressant, stimulant, or any narcotic drug, or any other controlled substance. That is a question you must answer in the negative on the CA form 4473 application to purchase a firearm. California's politically correct medical marijuana card has no legal effect against the federal drug laws making use or possession of marijuana a crime. Therefore, if you apply for such card, you are acknowledging your illegal under federal law use of the drug. Arguably, you become a prohibited person by doing so. A prohibited person is chargeable with a felony under federal law for even applying to purchase a firearm. You can make your own decision now.

Possession of a valid medical marijuana card does not prohibit you from owning a firearm.In your case, you would want, of course, to answer "no" on the DROS form when asked if you were an unlawful user of marijuana or addicted to it. You are a lawful user of marijuana, using marijuana for medicinal purposes. A positive answer could result in a denial pursuant to an unsatisfactory background check.