Do the same effects of different drugs stack? For instance, if an unaugmented mundane human with Reaction 3 speedballs a dose of cram and jazz, will they stack for a total of 3 Initiative Passes at Reaction 5?

Generally they'll stack unless they otherwise mention not stacking.
In the case of Cram and Jazz yes they stack, but have different durations.

Fantastic. Thank you.

Do they stack with cyber/bio-ware? (And can you quote some reference, please?)

I assume you mean the Cyberware/Bioware such as Reaction Enhancers, Wired Reflexes, Move by Wire, and Synaptic boosters.

No they don't.

Wired Reflexes and Reaction Enhancers both have a line (p342 SR4A) "Reaction Enhancers are incompatible with most other initiative-boosters" and "Wired reflexes cannot be combined with any other forms of Initiative enhancement except Reaction Enhancers."

Synaptic booster on p347 of SR4A: "The synaptic booster cannot be combined with any other form of Initiative enhancement."

Augmentation p 41. "Move-by-wire cannot be combined with any other form of Initiative enhancement except for Reaction enhancers."

And just as a note, Magic based increases.

Improved Reflexes Adept Power p196 SR4A: "The maximum rating of Improved Reflexes is 3, and the increase cannot be combined with technological or other magical increases to initiative."

Interestingly enough, Increase Reflexes the spell (p208 SR4A) has no such limitation written into the spell. It does however limit IPs to 4.

Thanks ProfGast. For some reason I thought that there should be some paragraph saying that enhancements acquired by drug (ab)use are not compatible with rest of reaction enhancements.

I guess I've been using a house rule, but on prior precedent, all IP adding effects do not stack with each other at my table.

Interestingly, if you can handle the overdose, if you take multiple doses of the same drug you get multiple bonuses, ie: taking 3 doses of Ripper you get +3 Strength, but you are taking a suggested 2 Physical damage from OD.

EDIT: The overdose may be wrong, but it's something like that.

I'm not sold on the 'stack the same drug' thing. Double doses of toxins don't do that, so why should drugs?

Of course, the whole incompatible mechanics of drugs and toxins is its own mess.

So getting hit twice with Narcoject doesn't deal 20S damage (minus successes on the Toxin Resistance Test, of course)?

Not quite, no.It (unfortunately) is left to the GM, with no guidance. That could mean double effect for double dose, but who knows? We talked about this in that other thread with burst-fire gel-capsules. And do you get to use your Body+[resistances] against each hit, since you said "hit twice with Narcoject"? Or does it work like burst-fire: +1 Power/dose? And so on.

There are other possibilities, as well. You could house-rule that the duration is increased (and the eventual crash), because those are 'other effects'. For some chemicals, the duration is already keyed to the Power (most drugs are X-Body), but others have set durations (CS gas).

I was talking about getting shot twice in the same IP with Narcoject, not burst fire.

But yeah, quoting the Concentration bit (where's that from? Arsenal? Page/book pweese) basically "answers" the question by saying "GM discretion," which is never a fun decision to reach on an online forum. It leaves too much unanswered.

Exactly, I agree. Stupid 'GM discretion'.

I mean, the same IP is essentially the same thing. If I take a pill, drink water, then take another, wash it down… did I take one double dose or two single doses? Shadowrun is weird because of the burst-fire rules, but it's still something we'd like to know about toxins/drugs (which, again, really deserve unified rules).

Oh, sorry. That's SR4A, p255.

Personally, based on no medical training, I feel like dosage-to-effect relationships aren't linear (in both direction). A double dose of ibuprofen doesn't do much more, but a double dose of hospital painkillers might be *more* than twice as strong (perhaps dangerously so). If reaction-boosters could be safely (even relatively speaking) used at a +2 dose, I feel like people would already be marketing them at that level.

Bah Yerameyhu, it's only a double dose if you take 2 of the pills with the same glass of water. If you just take them one after each other it's just 2 single doses and doubles the time the drug lasts..... It’s only simple logic.

Seriously though combining drugs is almost always seriously bad news. It should have multiple negative affects not just the negatives from both. Taking 2 initiative boosters and excepting them both to work should be a major/heart attack type effect, nm what it could do to your nervous system.

Well, one way that you get 'more the the sum of the drawbacks' could be adding any crash damage into a single damage resistance test (effectively halving your total dice). However, many drugs already do unresisted damage, so that doesn't help for them. The only real guidance I'm aware of is that speedballing multiple drugs increases the Addiction test Threshold; that doesn't really seem like enough, but how realistic to we want this game to be?

In reality, mixing drugs might simply kill you, or do permanent damage, or possibly nothing, or even work better together. Some of the SR4 drugs are *already* mixtures of drugs working together (Nitro, for example, has novacoke in it, but doesn't have the same effects as novacoke). What happens if you speedball them?

You become addicted to high volumes of techno-goblin-rock, of course.

Like, liters of it?

I meant decibels, but I guess that works too. Kinda.