Many employers have tested employees for signs of drug use, including marijuana, and have terminated employment if a test is positive over my lifetime.
I've had personal experience with these terminations, and the following is an excerpt from a LinkedIn article about it.
My employers were impressed by my desire and ambition; I had great performance assessments and was rewarded with training opportunities, promotions, prizes, and bonuses
I was once in charge of the permitting of a new uranium mine, which resulted in the creation of 28 new jobs, an accomplishment I am still proud of.
Despite my mental illness, I was able to attain these goals.