A skinny kid is looking at a few weeks for the joint they smoked to leave their system. An overweight person is looking at roughly 30 days. Obesity takes you in to ??? mark mode, as many as 90 days is plausible from what I've seen. That's just casual use, habitual users skew the math wildly. Why? THC metabolizes in to your fat cells, and sticks around.

Alcohol? Since it's typically just a urine test, you can expect the traces to be gone within hours. If they're doing a liver enzymes test, they can detect alcoholism or heavy alcohol use in a wider window, but it still doesn't compare to the time weed stays in you.

Further, alcohol abuse can generally be explained away because it's accepted by society. As long as you're not obviously drunk when talking with them about it, you can get a pass. Weed is the devil's herb, cause of all manner of calamity and reefer-madness, don't'cha'kno. There's no explaining testing positive for marijuana away.

As the article notes, the problem is how much longer weed stays in the system compared to other drugs.