Cocaine and heroin come from a plant. Are you suggesting that cocaine and heroin users should be able to possess a firearm?
Are you in agreement that felons should lose their Constitutional rights? Just not drug users?
States do not have the authority to override the US Constitution. The US Constitution, and Federal law, overrides State laws and State Constitutions. While it may be legal in a particular state, it is still Federally illegal. And you can be arrested by Federal agents. It is highly unlikely, though, because the the Feds have repeatedly said they’re not going to bother with potheads in states that allow it, but that option is always there.
I am all for States rights. The US is a Federalist Government, born from the same Constitution that includes your 2nd Amendment rights you spoke of.
We can change the Constitution so that the States have more control, so that they can override the Federal Government. But at this time, the States cannot determine how an individual loses their 2nd Amendment rights. The Federal Government does.
Let's change the Constitution. You only need 2/3 of the House, 2/3 of the Senate and 3/4 of the States to agree to change it. Go for it.