Experience of legalised drugs like alcohol suggests that you would see much wider mainstream use of drugs and associated medical conditions if you legalise it.
Even if prohibition is largely symbolic it does serve a purpose.
They will never legalise it simply because they would face billion dollar lawsuits from people damaged by the drugs...directly or indirectly.
Like the lawsuits the smoking industry has faced - which contributed billions to the coffers. And people still smoke.