You raise a valid point.
I currently have a person; loves his weed,(but is a binge drinker) worked in manufacturing 15 years ($33/hour), the company changed hands last year & drug screens were announced & scheduled 90 days in advance, and yet he would not stop toking for roughly 21 days prior to being tested. But— if you try to fire people for drug use, they can demand 21 days of inpatient. Instead, they just targeted his butt for a few months, he was tardy 3x’s and then they fired him for cause. (Now he’s on Medicaid and in a 12-step program.)
On the flip side of that equation; Big regional food-retailer here,(union shop) gave up on PRE-employment drug screens, cuz’ they couldn’t get enough applicants to fill the positions. (THC and opiates were most common)
They went to POST-ACCIDENT drug-screening regime. They don’t care what your hobby’s are, but if you have an accident at work, you get blood and hair-screened instantly. If you’re positive, you go into rehab or you resign voluntarily that day.)
I difference with heavy drinkers is that most can stay sober long enough to go to work, then drink on the weekend.
Dope heads think because you can’t smell it on their breath they will smoke dope before work.
I have never seen a “Former” heavy dope smoker like you do with drinkers. Nope, dope heads never give it up.