Sorry, I was commenting on a much later case, with Roberts and Alito sided with the majority, Thomas and Scalia dissenting, wherein the court ruled that “medical marijuana” laws did not nullify federal laws against marijuana, even when a person grew marijuana for his own purposes.
Are you thinking of Gonzales v. Raich? "Respondent Monson cultivates her own marijuana ..."
Stevens, J., delivered the opinion of the Court, in which Kennedy, Souter, Ginsburg, and Breyer, JJ., joined. Scalia, J., filed an opinion concurring in the judgment. O'Connor, J., filed a dissenting opinion, in which Rehnquist, C. J., and Thomas, J., joined as to all but Part III. Thomas, J., filed a dissenting opinion.
O'Connor's dissent is basically that the logic of Raich eviscerates the Gun-Free-School-Zones case, Lopez. She may or may not have been aware that Lopez was already eviscerated, and in any case, here general approach to "following the law" is to make policy decision, and effectively take over "making the law" into a form that suits her personal sensibilities.
Thomas's dissent cuts to the core of the issue, but if adopted, would put wide swaths of federal legislation and regulation on the junk heap (where they belong, but that's another matter entirely).
Respondents Diane Monson and Angel Raich use marijuana that has never been bought or sold, that has never crossed state lines, and that has had no demonstrable effect on the national market for marijuana. If Congress can regulate this under the Commerce Clause, then it can regulate virtually anything--and the Federal Government is no longer one of limited and enumerated powers.
Commerce clause aside, the Supreme Court has not met a federal gun regulation that it does not approve of. After it held the Gun_Free-School-Zone act to be "too much," Congress rewrote the act to include the phrase "or affects interstate commerce." Post-Lopez indictments on the new and improved GFSZ Act have been upheld. SCOTUS denies cert when those cases come before it.
Directly to the intersection of guns and the Raich decision, see the 9th Circuit Stewart case, which was decided under order to the 9th Circuit, from SCOTUS, to find Stewart in violation of federal gun regulations for possession of a homemade machine-gun - SCOTUS told the 9th Circuit to "follow Raich."