Final answer:
The peak year for marijuana use in the United States was 1979. Over the subsequent decades, there has been a significant shift in public opinion and state laws toward legalization and decriminalization of marijuana.
Step-by-step explanation:
The year that marijuana use in the United States reached its peak was 1979. The late 1970s witnessed some of the highest rates of marijuana usage, as the substance became more entrenched in American culture. While today's landscape is significantly different, with numerous states legalizing marijuana to varying degrees, the peak usage rate was seen decades ago.
Differing views on the legality and morality of marijuana have been a persistent part of American history since the early 1900s. Over the years, public opinion has dramatically shifted towards a more accepting stance on marijuana use, with recent movements focusing on legalization and decriminalization. Now, with a majority of states having legalized or decriminalized marijuana in some form, the U.S. has markedly changed its approach to this substance.