Drug Abuse in the US
Alcoholics 17.6 million
In a post-SHTF scenario, most illegal drugs will not be available. There will simply be no supply chain since people will not have money. Eventually that may change, but in the short run, expect chaos as suddenly many meth-heads can't score a deal. Heroin or morphine addicts will flip out.
Since 20% of the nation is disabled, and many are on pain medication, expect a switch to stealing pain meds. Many are already abusing them, and since they have no supply, then the natural way to get them is by breaking in. Since they don't know how to function in society well, and they can't get their medicine, and they can't earn money through their normal means, expect robberies anyway to get food and supplies and the occasional score of old prescription medications in cabinets.
17.6 million are alcoholics. Suddenly their legal drug of choice is cut off. That withdrawal will be very ugly. Since many forms of alcohol can be found in homes (some dangerous to drink since the alcohol is not ethanol and can cause blindness), expect break-ins to steal alcohol. Any alcohol in stores will be gone with 48 hours of warning. If that. Ethanol is a perfect barter item. It can clean wounds as well as offer a minor lift, so any alcoholic knowing how bad withdrawal is, will know to avoid it. It is particularly nasty. It can rapidly escalate to a medical emergency. I won't post any videos, but there are many which demonstrate delirium tremens and major health issues like seizures during the withdrawal. You won't have benzodiazipenes, the primary drug to assist them, so God bless you. If you're not a believer, I guarantee you that you'll be praying for relief for them.
If you have that problem, or have a family member who lives with you that does, I urge you to carefully include that aspect in your preparations. There's a lot of resources. It takes time for people to clean out. Expect them to fail, and realistically some of them will steal rather than go through it. The very best way is to taper off slowly now, but of course many of you can't or won't. The recidivism rate is enormous, and so even getting a handle on it, will be a problem forever.
Other drug abusers while psychologically addicted, will be able to taper off, but someone who can later offer them illegal drugs will be an enormous temptation. This poses just as much of an issue for survivors as a way for a criminal to gain new gang members in the short run.