I'm not American, so I'm curious as to why the prohibition of alcohol needed the Eighteenth Amendment.
I went through the full text of the United States Constitution and I can't seem to find anything in it stating that an amendment is required to ban alcohol. The United States Constitution also doesn't seem to mention any recreational drugs, whether alcohol or otherwise.
When other recreational drugs were banned with the Controlled Substances Act of 1970, a constitutional amendment wasn't required for that. Why did the prohibition of alcohol need a constitutional amendment but the prohibition of other recreational drugs didn't?