fauna lore makes most of those 3 skills again.
A lot depends on stability of a toxin and how good the directions are.
A stable toxin thats well understood so it has good directions is easy.
Case and point:
"Roundup". . .spray directly on weeds, wear gloves, wash hands thouroghly after using, wear mask if spraying extensively. Use away from face, do not inhale, drink or ingest. Keep out of reach of children. Active shelf life 2 years.
The annoying to use poisons will be 1) The ones that degrade fast so they need to be obtained prepared and used fast. . .like most snake venoms, that are protien or enzyme based and will degrade fast out of the snake if not kept airtight and/or refrigerated. 2) the ones that you want someone to ingest and be affected without anyone knowing they were poisoned or 3) having a specific non lethal effect on someone.
The vast majority of poisons would fall under the "Are you mentally capable of dipping a french fry in ketchup?" and/or the "Do you know how to open a bottle and pour?" category. . . .
Poisoning an arrow/knife is not rocket science, and the odds of poisoning yourself are close to zero if you take basic precautions and do it sober.
If Joe villian hands Jim the assassin a small jar of a black tarry substance and says "Dip your arrows in this just before you shoot the king" does anyone really think that Jim the assassin should be making a skill roll to do so? At worst, if this is not a rushed situation, I might perhaps make Jim roll an agility maneuver of the "Don't roll open ended down" variety.
If Sam villian hands Sandy sabateur a jug with a cork in it and says "Go and pour this into the well at the royal barracks, don't get any on yourself or you'll die." do you really think Sandy needs to roll a skill for that? If he's not rushed, and takes his time, and wears gloves, it seems almost impossible for him to fail. . .another, perhaps "Roll an agility maneuver and don't roll open ended down."
90% of instances where you'd use poison, it's akin to having a "Put toothpaste on toothbrush" skill, or a "pouring a bottle of beer in a cup without spilling" skill.
The complexities and subtleties of poison involve a tiny minority of all instances where someone would use it in a game. . . .Non lethal drugs, where you want someone to behave in a certain way, or fall asleep for a given duration. . . .those would be uses of an art, a skill, and a freaking hard one. . . .even knowing your exact body weight, using pure and very safe drugs, with O2 masks and defribulators a certain tiny number of people die in anesthesia. . .it's hard to guestimate bodyweight using impure drugs to get a chosen reaction. . .and that's pharmacology, or "Herbalism". . . .I have serious doubts about poison use as a skill at all.
The best call for it I can think of is the "I want the poison to be undetectable, and I want everyone to think he had a stroke" kind of thing. . .and that still feels more like the dark side of medicine/herbalism than a poison skill.