Begining in 1941 and continuing through the 1940's the Supreme Court gave us our modern definition of the Commerce Clause of the US Constitution through several cases, most notably United States v. Darby Lumber Co., 312 U.S. 100 (1941); United States v. Wrightwood Dairy Co., 315 U.S. 110 (1942); and Wickard v. Filburn, 317 U.S. 111 (1942).

Those cases stood for the proposition that the Commerce Clause allowed the Federal Government to regulate intrastate behavior if that behavior could have any impact out of state. That's a very broad view, and has been interpreted even more broadly to include the regulation of narcotics on a national level, even if those narcotics were wholly produced and consumed in state. See Gonzales v. Raich, 545 U.S. 1 (2005).

But those cases were a radical departure from the previous constitutional view on the Commerce Clause. The only legal view on it prior to 1941 is best summed up by the following quote:

Thus, Congress having power to regulate commerce with foreign nations, and among the several states and with the Indian tribes, may without doubt provide for granting coasting licenses, licenses to pilots, licenses to trade with the Indians, and any other licenses necessary or proper for the exercise of that great and extensive power, and the same observation is applicable to every other power of Congress to the exercise of which the granting of licenses may be incident. All such licenses confer authority and give rights to the licensee.

But very different considerations apply to the internal commerce or domestic trade of the states. Over this commerce and trade Congress has no power of regulation nor any direct control. This power belongs exclusively to the states. No interference by Congress with the business of citizens transacted within a state is warranted by the Constitution except such as is strictly incidental to the exercise of powers clearly granted to the legislature. The power to authorize a business within a state is plainly repugnant to the exclusive power of the state over the same subject. - License Tax Cases, 72 U.S. 462 (1866).

In other words, prior to 1941 Congress was expressly forbidden from banning, or even attempting to regulate any activity that occurred wholly within a state.

The 18th Amendment was passed in 1920. Although there would have been no question that Congress could have banned the sale of alcohol across state lines, the constitutional view at the time was that Congress had no power to regulate alcohol which was produced and consumed within the same state. See Hoke v. United States, 227 U.S. 308 (1913) - holding that Congress could ban interstate prostitution even if that prostitution was legal in all states where the activity occurred.

The promoters of prohibition didn't just want a ban on interstate alcohol - they wanted a national ban. The only way to guarantee that was to remove the states' authority to make alcohol legal. The result of that was the 18th Amendment.

By the time of the Controlled Substances Act the view on the extent of the powers given to Congress by the Commerce Clause had changed to become so expansive that there was no serious debate as to its constitutionality.