What you will find by 2020 is a very likely quickly changed landscape where recreational cannabis is more widely available in states the AT passes. I'm sure with Mass and ME now legalizing recreational cannabis dispensaries will locate near the AT to serve the AT user market as part of their market and that's only the two states in the east that I know of that has legalized recreational use. With these two states legalizing rec use legal stigmatization concerning cannabis use is sure to lessen. It's very likely within the next three yrs additional east coast states will legalize rec use.
On the more generally liberal west coast, on the PCT that passes through three states that all have legalized rec use you will not find many thru-hikers that drink heavily but there sure is significant current weed use. The weed culture sentiments are much much more relaxed on the west coast and on the west coast trails than the east coast and it's trails.
What I've seen on the AT in the last dozen or so yrs alcohol use is largely confined to in town visits and near THs at busier road crossings and maybe some of the larger established camping areas. And weed users, because rec use is still largely illegal, tend to have much greater reluctance to publicly use around others hiking. That may change as legalization continues in the east.
Although some don't think of drug use this way I recognize the largest drug or drug category used on the AT is not weed, alcohol, caffeine, or tobacco but pain relievers and anti-inflammatories such as Motrin(Ibuprofen), other NSAIDS, and prescription drugs overall, including massive amounts of pain prescription meds. Notice how drugs are conveniently called meds when they come from the pharmaceutical industry?
SO MANY will point fingers at others doing drugs when the drugs being used are more socially unacceptable while ignoring their own less stigmaticed drug use.
Hopefully, this info can help those hike soberly.