The main mentally incapacitating drug in this country is and always has been alcohol. Alcohol was banned roughly between 1919 and 1933. It was first banned because ostensibly grain was needed to feed the troops during WWI. Which causes one to ask: did soldiers eat more grain after being inducted into the military than before? The Ku Klux Klan was a major supporter of Prohibition.
Addiction is a physical condition. Treating it as a crime rather than as a health problem has never caused the number of addicts to decline. Many, if not most, people addicted to opiates today started out with prescriptions for Oxycontin, produced by the Sackler family's Perdue Pharmaceuticals. It was falsely promoted as non addictive, but in reality it was simply a far more expensive drug than heroin or morphine. Not one of the Sacklers has been indicted or convicted.
Why are humans designed to be addicted? Who made them that way? Why, God, of course.