Guns are all about federal laws, under federal law it is illegal to even possess a firearm if you use what is considered "illegal drugs" under federal law. But, as far as I know there is no federal database of card holders so it may not come up under a check, but if the state has this record, which I know they do, I imagine at some point during that background check this fact would pop up and be seen on the federal end. You need someone from California that actually knows the laws to answer this.