The poskim have not created an issur. They simply applied it. That is why the issur of chovel be’atzmo or venishmartem which always existed were not followed with regards to smoking in earlier years. In fact, all of Torah shebe’al peh is the application and derivation of halachos of life from Torah. No one is creating gezairos (though Rabenu Gershom did precisely that with bigamy, privacy, and forced gittin).
Alcohol does not damage the brain. It affects the brain, and the brain recovers from the effects. The brain damage from alcohol is irreversible. Check with any neurologist or addiction professional. If it damaged anything, the halachos of chovel etc. would be relevant.
I could get into piercings, but I’m fear dragging this thread into other directions. Simply put, piercings have always been done, and we find it in Torah as well. If a piercing is done irresponsibly, there is risk of infection, and would fall into the halachic categories mentioned earlier. This is an issue with some teens at risk who cannot get parental permission or funding to get these done, who then choose to do it themselves. This would be assur, not by my decree, but by simply applying known issurim and their criteria.