Medicinal distribution

I'm thinking. For once.

+1A
Best used on units with less attacks, as it gives them a higher damage raise (hellions gain +50% damage, going from 2 to 3 attacks, while wyches gain +33%, going from 3 to 4). this effect has diminishing returns, so use it on the units that hit hard in a few attacks. Not great on wyches, prioritise hellions. wyches are next priority. very poor on a succubus, only +25% boost, she does much better with other drugs.

+1S
This one is the trickiest. Definitely not reavers. gives wyches a +50% dmg boost against T4, +33% against T3, nothing for T5, +100% against T6 and 7, and no more benefits. so use +1 S on wyches if they will face lots of T6 and 7 monsters especially, or if they face T4. for cursed blade, use if they face T8 & 9, or T5.

For hellions, use it on them if they face T5, T8 & T9


+2 move
the cardio succubus, or makes reavers even better. also ok on hellions. Wyches should be in transports.

+1T
use on reavers, or tarpit wyches.

+1 WS
the dud drug. only have an effect on units that will charge before T3, so use on reavers and hellions if you have to. only grants a + 25% dmg boost to 3+ to hit.

+2Ld
Beastmasters. otherwise, big blobs of wyches. the other dud drug.

Unit drug priorities

Wyches
1. +1 S for T4 killing and monster threatening.
2. +1 A, if you have used +1 S, this is the second best drug for wyches.
3. +1 T, good for tarpits. T4 4++ is surprisingly resilient.
4. +2 Move, helps for that little extra disembark, although you only use it on the turn before you charge. ok for footsloggers.
5. +1 LD good for blobs, although footslog lists SHOULD be running cursed blade, which negates this.
6. +1 WS, the wyches probably won't get in before this does too much, you will only use it for one turn before pfp kicks in.

Reavers
1. +1 T for tankiness
2. +2 mv, really guarantee that charge, especially with red grief.
3. +1 WS, the only unit that can use it.
4. +1 A, better on other units but ok if you run a large unit. bad on MSU.
5. +2 LD, ok if you have a blob, but useless on MSU.
6. +1 S, has 0 effect.

Hellions
1. +1 A, these guys get +50% dmg from this.
2. +1 S, get much better against T5, and a bit better against T4. also get 100% bonus against T8 & T9, so go try and kill some vehicles.
3. +1 T, gives them some small arms protection, these guys really need resilience and while this isn't great, it is better than nothing. combined with hunt from the shadows or lightning fast reflexes, these guys can be surprisingly tough.
4. +2 move, ok for flying up the board and with red grief.
5. +1 WS, ok if they get a T1 charge of with red grief.
6. +2 LD, these guys are too expensive to die, by the time this comes in to effect, the hellions are dead.

Succubus
1. +2 move, not useful on much else, and she will probably be footslogging.
2. +1 S, really helps her threaten larger targets with S6, she can also mulch through T3 characters or blobs. also helps her against T6. (also T10, but please don't send her at superheavies). pointless on the whip builds.
3. +1 T, helps prevent warlord, ok for tar pitting, and the survivability doesnt hurt. better on reavers though.
4. +1 WS, not great, i saw on a rules thread that this technically doesn't benefit her glaive. also pointless on non-glaive builds.
5. +1 A, only give +25% boost, better used on other units.
6. +2 LD, she doesnt get to use this.

Beastmaster
Just use LD. really.

Mostly agree with your assessments, pretty much on point. Only thing I'd say is that +1 strength on hellions is really useful, anything that's multiple wounds that you want the to hit is going to be t4 or greater, so the strength is always going to come in handy except against t6 and 7.

Obsessions changes these priorities up a bit, mainly cursed blade since that will provide the strength boost for wyches/hellions, making the strength drug less important. s5 wyches would be pretty cool, but I think 4 attacks s4 would be better.

The difficult with distributing combat drugs though of course is when you have multiple units. If you're taking say 2-3 wych units the choice becomes more difficult, since ideally yeah you'd want to boost all of their strength/attacks but can't. I suppose it's worth considering rolling in some cases, but I think the only time I'd do that is with a succubus with the extra combat drugs trait/relic, since after selecting say 3 drugs for your units it would be tough to have anything good left for 2 more selections on the succubus, and chances are at least one of your rolls will be decent.

Mostly ok, But I agree with Lord asvaldir, there are some details that change everything.

The most obvious being the choice of obsession. if you already have the s or a boost you don't need that drug as much. What units you have, you can have multiple of the same unit and tailer your units for specific roles.
Giving wyches +1 thoughness or +2 move makes them more of a objective grabber/disrupter, while +1 a/s makes them offensive.
Although the enemies also play a large part (lots of s3, no need to give t5 to your reavers, mostly t5 enemies no need to give wyches s4 etc)

I like the WS one on the glaive succubus to cancel out its negative. Only relevant for first two turns, but whatevs.

Also, am I correct in thinking that a stimm addict lets you pick all 6 drugs easier since it picks 2? I.e. only will take 5 units before you can unlock the same drug again.

That would be correct I think, which matters for a cult heavy army.