If I was you then, I’d do the usual titration of taking 100ug every hour-3hrs until you get there.
Big waste of acid. Redosing within something like 72 hours has much less effect, and you'll get more of the adrenergic and other unpleasantness rather than the desired effects at 5HT. If you must take the acid, you'll have to titrate and find the desired dose over a pretty extended period of time. Please don't jump into taking a shitton of tabs at once, though.
Don't listen to the people hear throwing out numbers of how much you should take.
I deliberately say "tabs" rather than a putative dose in μg because doses claimed for commercial acid are about 99% pure bullshit (even if you know for a fact the dose that was laid, it also degrades.) Bit of a pet peeve for me. People have this assumption that 1 typical tab is 100 μg as a rule of thumb, and that's simply not true. 100 μg is a lot stronger than people imagine it to be (speaking as someone who's privileged to know exactly what mics feel like.)
But I digress. As for Risperdal, it is a particularly effective (or problematic, depending on your perspective) neuroleptic in terms of blocking LSD, perhaps even better than Thorazine, which is usually recommended by people who are familiar with psychedelics, and was the drug of choice to abort trips dating back to Tim Leary. Haldol, the usual go-to, along with Ativan, for psychotic agitation in hospital emergency departments, is not as good as either. An atypical is not a bad choice though—I'd go with Zyprexa, Risperdal isn't that quick acting and isn't available for injection–but I'm a traditionalist at heart, I'd probably stick with Thorazine, 50mg i.m., repeatedly if necessary. That's what Dr. Leary himself suggested in
The Psychedelic Experience, and though he was wrong about a lot of things, this isn't one of them.
Risperdal, along with the other modern atypical antipsychotics to one degree or another, is especially effective in blocking LSD because of its antiserotinergic effects. Thorazine has more of this as well compared to most of the older typical drugs. Thorazine and LSD are both "promiscuous" in the brain—they effect just about every receptor, just in different directions.
For a person taking Risperdal contemplating an acid trip, I'd be wary due to the underlying condition that this drug is there to treat. I'm glad to hear that the option of simply skipping the dose isn't what we're talking about here—that would be dangerous, we'd be dealing not only with a person with underlying psychiatric issues taking LSD but a person with those predisposition in a state of neurochemical "rebound" from the neuroleptic. Bad news.
Further bad news is as I touched on before some of the promiscuous effects of LSD I mentioned above with respect to receptors other than serotonin and dopamine will be in full high-dose swing before you get the desired 5HT/D2 effects. This will possibly lead to unpleasant body load, anxiety, and peripheral effects. Adrenergic effects, for example, of LSD are minimal at low doses but significant at high doses. Not as badly as some of the phenetylamines which can actually cause serious vasoconstriction, but it enough to be noticeable and potentially contribute to a bad time. In terms of these receptors you'll be taking a huge dose even if most of that dose is blocked in terms of the receptors you really want to hit. In fact, the effects on each receptors reach a plateau eventually, different for each one.
Beyond about 1.4mg of LSD, the effects you're getting as you increase the dose are more and more peripheral and less serotonergic/dopamonergic. Basically what
@SnafuInTheVoid was saying. Yes, this means kids taking a couple strips at a time are just wasting good L, and setting themselves up for negative effects with no upside. Sometimes they're doing this after getting spun for days and building tolerance. They're still going to get proportinately more bad effects than good, even if they need to overcome tolerance. Basically same thing for you if you're taking Risperdal and needing to overcome receptor blockade. Subjectively, even if you clear the receptor blockade, the experience is likely
still going to be attenuated. Even more so at extreme doses.
Unfortunately, as a bottom line, I wouldn't drop acid on risperidone, period, both because it's dangerous due to underlying issues and also because it's potentially just not worth it. It can be done but even if you don't get a negative outcome you may not get what you want. I'd pass.
But to reiterate, the responsible way to do this would be to start with maybe no more than twice a typical dose—assuming you've tried a typical dose and gotten nothing, otherwise maybe a typical dose just to be safe—and see what effects you get, wait several days, increase the dose, rinse, wash, repeat. Increase by one, maybe two at the max if and when you're taking a bunch, dosage units per session. Be careful though, it can sneak up on you. Definitely don't redose in the same session. Waste of L at best.
When tapering up, be particularly mindful of any body load, peripheral effects, etc.—any effects you feel although they're not tripping in the usual sense—you might be experiencing, and be aware that pleasant or not you'll have to deal with them, probably worse in fact, when you get fully tapered up.
All in all I'd still maintain that it's still a risky proposition. I think I've outlined a proper harm reduction approach, though. Don't expect the acid trip to equal any trips you might remember from before being on meds, though. Just being honest. However above all, don't discontinue the meds, especially abruptly. If the meds are an issue, discontinuation or changes need to be done with a doctor. I'm not even saying this as some kind of disclaimer, it really is a potentially dangerous situation.
As for the bigger question of going off meds, I've seen this phenomenon clinically more times than I can count—almost invariably, the patient feels much better after stopping the meds, especially after the first few days or week as it gets totally out of their system. They'll usually be feeling OK, maybe even "more themselves." After all, they have side effects and a generic dampening effect on consciousness. Yuck, right?
However, equally invariably, sometimes weeks or months later, there's a relapse to the mental illness. And it tends to be worse than before—research proves this, in schizophrenia at least—each run of stopping and going without meds makes the baseline a little worse. There's a permanent and cumulative effect on the brain.
The eventual kicker is that the patient, having felt better initially coming off meds, and then some time later becoming acutely ill, often doesn't, or outright refuses to, make the connection between stopping meds and having a crisis some time later. Nonetheless there's a cause and effect. Because it's not immediate, because the patient often doesn't want to believe they need medication, and because the nature of many psychiatric illness includes being unaware that one is ill.
TL;DR: Some good, some bad advice in this thread. I'd recommend against tripping period but if you must, try increasing your dose gradually over a few sessions, spread out over a few days. Don't under any circumstances just swallow an arbitrary number of doses someone suggested.