Poisons are the bane of a GM's life. Something small, cheap, virtually undetectable, and that can kill a foe with pretty much no recourse or chance to overcome the effects, while the attacker is safely in another room, city, or even kingdom, is anathema to the whole concept of dramatic battles and engaging the enemy fair and square.
So much so that the venerable first edition of Advanced Dungeons & Dragons included a couple of pages of information about how difficult, time-consuming, and expensive it is to make or buy poisons, how ineffective they are at actually hurting people, and how if you put them on weapons they basically just slide off and quickly become useless. The goal of course was to discourage players from wanting to use poison, to avoid all of the game-breaking things that can happen when you let PCs use it with abandon.
Not that this ever stopped anyone from wanting to try it.
C-3PO: Are we there yet?
R2-D2: I've missed the whole ending of the adventure? Again? This is just like the fantasy campaign!
GM: Yes, it's your own fault again.
R2-D2: It was never my fault the first time. My analysis of that logic puzzle was flawless.
Obi-Wan: So how come you died?
R2-D2: See this? This is the chapter on poisons.
R2-D2: I know every page of this backwards, and I'm telling you, there is no such thing as immunity to iocane powder!
Anakin: If you hate playing so much, why are you even here?
R2-D2: Well... this is the best game I've ever played in.
GM: Thank you. I think.
R2-D2: Now if this science fiction campaign only had a massive battle involving space dreadnoughts bristling with atomic missiles.
GM: Hmmm. <scribble>
Anakin: As long as we're the ones with the dreadnoughts.