Well, 25 years of practicing Witchcraft (including coven initiation, and having been part of many groups and events), this question had me going, "Wait... what?" 0.o
The truth about Witchcraft is that we simply don't believe such things. Most Witches don't believe in demons because they're not Christian, they're Pagan. The whole fallen angel thing doesn't come from our religions.
And Witchcraft generally isn't about conjuring/contacting any such things. That's more something in the realm of Ceremonial Magic (High Magic), which has some roots in Judeo-Christian beliefs. Witchcraft is Low Magic, it's nature magic. We see it as a tool-- like fire, which can heat your home or burn it down. But it's not good or evil, it's just a part of nature, and you need to learn how to use it respectfully and with caution.
And probably just because I am not a drug user myself, I've never actually had any Witches in my groups or as a friend who did drugs. If one did, I'd urge them to get help for addiction, but things like meth just don't come up in my circles of acquaintances.