The active component in marijuana that people find so desirable was not really known until the 1960s when a research team in Israel found that after injecting THC into aggressive rhesus monkeys, they became calm and sedate.

The primary problem with the current available cannabis is that the THC content is not like it used to be. Prior to the 1990s it was less than 2%
In 2017 the most popular strains found in dispensaries in Colorado had a range of THC content from 17–28%
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6312155/