Any solid articles/advice/etc. about writing from the perspective of drug use? I'm looking to slip one of my characters a hallucinogen.
Draw on personal experience, or if you have none of that and don't want any of that, interview people. Research pays off. Pulling things out of your ass from imagination and cliche can be fun as a writer, but reads painfully to others. I also like to lurk Erowid pages and forums for people describing the qualia of particular intoxications, since I'm not especially adventurous myself.
As I understand it, most hallucinogens don't cause people to see things that aren't there; they alter their perception of what is there in front of them. So, something like LSD doesn't invent images like a dream. It intensifies and changes how your brain perceives the regular sensory data you're getting from what's around you. The devil doesn't just appear to you in a top hat with an army of flamingos. But patterns and colors might start to behave strangely and become otherworldly. Something to consider and be wary of if you're interested in verisimilitude. Maybe do some research and pick a substance that can do those things if that's what you were hoping to get out of it. I googled and found a thread of stoners discussing the particularities of different hallucinogens: here.
My oldest workshop submission has one of my characters tripping on acid. I mostly tried to stay true to the altering-what's-already-in-front-of-you business. The genre is magic realism though, he's in the middle of a nervous breakdown, he's on a cocktail of things, and I hid the smoking gun so to speak so a lot of things that seem to be hallucinations from nowhere turn out to be distortions of ordinary things. Given all that, certain options were available to me that probably woudn't work otherwise while aiming for realism.
When you're considering powerful hallucinogens, one of the more common experiences in a "bad trip" (if that's what you're going for) is the concept of dreams and thoughts becoming incredibly vivid. Like Bethwenn said, there's the concept of reality becoming less realistic is absolutely true. However, while it's also true that random crazy people you've never met will be unlikely to appear, it's also true that any phobias or thoughts your character already has will become intensely more real, sort of like how a dream works.
So if your character has a phobia of deep water, a hallucinogen could make this phobia far more profound and realistic. This character might begin experiencing feelings of drowning or a terrible apprehension about a shark attack while lying in bed on their second floor apartment. It's not rational, and the character might even realize that it's not rational, but hallucinogens affect the unconscious parts of the brain far more than they do the rational parts. A person who is afraid of clowns might begin to "see" clown make-up on other people, not necessarily as brightly colored greasepaint, but rather in certain facial features that their brain has difficulty interpreting, such as a smile or even the slightest waver in their gait.
In other words, imagine that every experience has a deadline which signals when the brain must accept what it's experiencing. In the time before the deadline, the brain has the opportunity to entertain multiple interpretations of what could be happening, and must arrive at a conclusion by the deadline. A hallucinogen significantly shortens that deadline, so that the brain, for all intents and purposes, is more prone to accept something as true that it normally wouldn't, because it's making the decision and attempting to rationalize an experience far more quickly and with far less grace than usual. This leads the brain to come to sensory conclusions that are far crazier than are actually true.
Hope that helps.
Ah, the Three D's: Drinking, Drugs, and Dreams.
These are just my opinions, so take them with giant, pretzel-salt-sized grains.
Oftentimes, the D's are handled in such a way where the writer's intent is to make the reader feel like THEY are drunk/dreaming/tripping. To really explain the visceral experience of being altered. I think this is rarely successful. It feels, most times, that the reader is the designated driver at a party where everyone is SUPER wasted. Everyone else is having a great time, they're funny, handsome, weird, whatever, and the driver is sighing and just waiting to go home.
That's why my big advice is to keep it brief. Don't make the reader plow through too much before we get whatever payoff.
Also, again, just advice, I think this is a great place to use a redemptive voice. A voice where the narrator is looking back at an event and telling the story the way they would to a good friend: "I didn't know it then, but now I know..." I feel like this allows you to be a little wilder with the descriptions, but also to describe things in detail, with the clearheadedness that comes with the event happening in the past. You're able to carry the reader through the scene without abandoning them entirely because your narrator is in a state that doesn't allow for creating much structure.
I know some people would hate that, and that style may not fit with your story at all, so feel free to totally ignore that advice. But if you're struggling, I'd recommend writing the scene up as if your narrator was describing what happened last night, and see where it takes you.
From my own experience, different substances produce very different alterations to an individuals conciousness. Doseage, setting, and intent are critical factors. You described "slipping" a character something. Being administered a hallucinogen unknowingly can have very negative results. LSD and some of it's neighbors are very powerful substances and not well suited inexperienced users. Others can be so subtle as to go almost unnoticed.