It reduced consumptions and reduced hospital visits because who is going to admit to breaking the law? Fun fact, criminals usually don’t go to the hospital for injuries sustained from their crimes, or report their crimes to the authorities.
Further the major economic issues came after the prohibition. The Great Depression started in 1929 and prohibition started in 1919.
Also banning alcohol absolutely did not reduce crime. Alcohol sales increased by several thousand percent before prohibition was enacted as people stocked up. Moonshining was a massive career and pastime. The mafia was making a killing off of created, moving, and selling alcohol, speakeasies we’re extremely common and everywhere.
Also again; who would report their illegal drug usage to the authorities??? Of course consumption would “decrease”. And if the police does not hunt down or prosecute drug users, then of course the “crime rate would decrease”, in the example of China. Do you think Chinese police are scouring the lower levels of Shanghai and Nanking and doing massive drug sweeps every Tuesday?
Banning things has never, and will never be an effective solution. This has been shown time and time throughout history.