So, I suppose I'll chime in on this one as well, since I have relevant experience. This does require breaking my anonymity a bit, since at least one person in the forum knows me IRL, which is OK. I'm Type 1 (although weird) and a recovering addict. I've been clean and sober since my early twenties, more than twenty years ago. I've only been diabetic for about a year, and am not yet on insulin, so...
Anyhow, I thought I was a heroin addict in my teens, and a coke addict about twenty years of age, and I did plenty of meth when I could (wasn't that common in the 80s and 90s where I lived). I never thought of myself as a drunk until after I got out of rehab a couple of times and genuinely tried to live without heroin, coke, weed, or other drugs. I was totally convinced that alcohol couldn't possibly be a problem. I found out over a couple of years that that was not the case. I became homeless because of alcohol and my inability to not drink, even though I wanted to not drink. I lost a child, a marriage, school, several jobs, and the love and respect of my family of origin. I wasn't one of those "staying on friends' couches" kind of homeless guys, I was a bum: drinking from a brown paper bag and sleeping on benches and in doorways. I didn't have any friends anyways at that point.
I don't know "what happened," but even though I was an atheist (still am, pretty much, although I prefer "agnostic" as a term these days), I asked for help from someone I knew in AA, and I haven't had a drink (or gotten high) since then. I still go to meetings, I sponsor people in "the program," and I'm even married to someone I met in the program. I've also gone back to school, made money, ended up with a PhD, and have a career as a government scientist (although that's not looking great these days...). I'm happy (well, generally), sober, useful, my family loves me, my son adores me, and my ex-wife hasn't tried to kill me in well over a decade. So things are looking up.
As for AA itself (or NA, or other twelve step programs), there is a lot of misinformation out there. My experience is pretty straightforward: although there is talk of Higher Powers and God, it's always in the context of "God of your understanding." It's never been a problem for me as an agnostic/atheist/non-believer: I have a conception of a higher power that works for me; no-one in AA has ever treated me differently because of my beliefs (even religious people); and I've managed to help other men recover over the years, some of whom were religious. As the book (the "Big Book") says, "there is no friction among us over such matters." That passage continues with this paragraph, which I think is important:
We think it no concern of ours what religious bodies our members identify themselves with as individuals. This should be an entirely personal affair which each one decides for himself in the light of past associations, or his present choice. Not all of us have joined religious bodies, but most of us favor such memberships
That was written in 1937, and I suspect the last clause "most of us favor such memberships" probably isn't true anymore, at least worldwide. 90% of people I know who are long-time sober in AA (10+ years) are not "religious" in the sense many Americans are. That's anecdotal, but it is my experience.
As for drugs and AA, I'll share some experience and some of my own thoughts. What @Robert17 suggests above is definitely not true, at all. AA is not only for those who are addicted to gin, vodka, and whiskey, although I have to admit Gin did me far more damage than heroin did. One of our founders (Bill W) had problems with drugs as well as alcohol. One of the earliest members, who helped to write the book, was a heroin addict, gay, a crossdresser, and a prostitute. And black. And AA accepted him with open arms in 1939, and he lived a long, happy, sober, productive life after quitting drinking and getting high. The Traditions of AA make it very clear that our "primary purpose" is to carry the message to other alcoholics. Some groups and many individuals recognize that drug addiction and alcoholism are related (some people think of them as symptoms of the same underlying disorder), and I've never yet encountered a group (and I've been to hundreds in all states of the US and about 10 countries abroad) that would say someone who had a drug problem and also a drinking problem wouldn't be welcome.
That being said, there is one distinction about drug addiction that I feel is important. For me, drinking leads to drugs and drug use leads to drinking. For almost all alcoholics I know, this is also true. Like most people in AA, I do not consider refraining from drinking but using other drugs the same as being sober (the use of medically supervised prescription drugs being an exception, although for me opioid painkillers are super dangerous and I avoid them like the plague). That being said, I won't sponsor someone who tells me "I am a heroin addict, but I can drink normally, and I'd like to continue having a beer on the weekend." For those folks, I strongly suggest they go to NA or seek help in other places. Why? Not because I think they are bad people (I don't have a moral stance on drinking or drug use), not because I think they are bad alcoholics or doomed, or anything like that. I won't sponsor them and suggest they seek help elsewhere because I don't have any experience with that kind of problem. Someone that can drink responsibly and not use drugs responsibly is a different kettle of fish, and certainly not an alcoholic. Using drugs doesn't mean you are not an alcoholic, but if you aren't an alcoholic at all, then AA is very likely not the place for you
There are people who "have a desire to stop drinking," are drug addicts, use the Program in AA to get sober, and live happy, long, productive lives. I (and most other AA members) have zero issues with such people. I'm probably one of those people myself, although I consider myself a "real alcoholic" and a drug addict (if they are indeed different issues, which I'm not convinced of).
Also, there are assholes in AA. I'd say not most, but there are plenty. There are cranky old bastards who think anyone who has smoked a joint doesn't belong. There are other cranky old people (mostly old bastards) who think that only Jesus can be the key to long-term sobriety. All I can say is this: there really aren't that many of those folks, and they don't speak for all of us or AA as a whole. The entire purpose of AA is to help ourselves by helping others. It's why I still go to meetings even though I've been sober longer than I drank and got high and more than half my life: I can find newcomers there to help.
tl;dr: AA can certainly be relevant to many people that use drugs, although it can be a leap for many (especially) young people to see that as true. I did a lot of drugs, and AA saved my life. I also recognize that I'm an alcoholic and a drug addict, and that is not true of everyone. AA has a long tradition of suggesting that people find what works for them, and we have "no monopoly on recovery." It's just a way that works for me and many others. It's not the best, only, or even a good solution to problems with drugs and alcohol. It's just my solution.
P.S. I genuinely fear the day I start insulin therapy, because I have both a love and a mortal fear of needles. My heart rate goes up when I see a needle on TV, in Walmart in the pharmacy, or when I get my blood drawn. I had to stop watching The Wire because I started to dream of using heroin again, almost twenty years after the last time I fixed. I used to steal my grandmother's insulin needles so that I could get high...I genuinely fear the day I start insulin therapy, and my wife fears for me too (she knows how touchy and sensitive I am about needles). It scares me to death.
P.S.S. I'm not trying to preach, I'm not trying to say AA (or 12 step programs in general) are good. I'm just sharing my experience with being a diabetic and a drug addict and an alcoholic. Hopefully it can do someone some good.