Final answer:
The Controlled Substances Act (CSA) was enacted in 1970, declaring the sale of marijuana a prosecutable act, with the U.S. government maintaining the right to prosecute recreational use despite medical use being tolerated.
Step-by-step explanation:
The Controlled Substances Act (CSA) was enacted in the year 1970. This legislation, passed by Congress, categorizes marijuana, along with various other substances, as a dangerous drug and prohibits its sale, deeming it a prosecutable offense. The federal government relies on state cooperation to enforce the CSA; however, although the use of marijuana for medical purposes has not led to prosecutions, the Justice Department retains the right to prosecute recreational use, as clarified by a 2013 memo from then-Deputy Attorney General James Cole.