And to answer RARodger's question, It depends upon what kind of poison you are making. Belladonna can be diluted. People used to put it in their eyes to produce that beautiful glassy eyed effect. I think risin just kills you.
a varient of this spell might produce the healing effects of alloe.
Belladonna in that application also acts as a mild neuro toxin forcing the pupils to dilate which also happens when a person's adrenalin (and other hormones) are up. It was very effective as a "cosemetice" because (it is theorized) that the human respones to dilated pupils is just as hardwired into your system as when they see certain expressions showing the whites of the view-ee's eyes.
I've acutally seen some papers on this in American Scientist. I'll send ref's privately if interested.
As for ricin -- oooo nasty juju! It is the result of making castor oil. The way it works is that it is a protien inhibitor -- it prvents the cells from creating protiens -- and thus leads to necrosis. In very small doses, one can recover from it as the dead cells are replaced faster than they are killed. Most cases result in permanent damage (think of it like permanent -X to STA and -X to STR) or death. Really nasty stuff.
Frankly, the rules in ArM5 for poisons and toxins need to be expanded/adjusted is such a manner and there is a real question here on effects of these things on Essential Nature. Some of thes toxins stay with you for the entirety of your (shortened) life. Since there is no cell or germ theory in ArM, things like lead and mercury poisoning (as well as oter metals like copper and silver) can probably be represented as either a permanent damage to the balance of humors (Ess Nat, again) or maybe some sort of disease that just happens to be associated with miners and users of the metals.
One thing I know for certain: even with modern medicine, biological damage due to metal poinsoning or neurotoxins does not heal easily if at all.
-K!
What???
How do you figure?
I've got to hear this.
It's obvious poison ivy is a plat that is bad...Alloe is a plant that is good... They are both plants. Thats more relation then some post I've read.
You that have yet to experience nettle need to get outside more, it's actually a pretty common weed. If you are gifted with this experience, keep in mind, that like with jelly fish stings, vinegar seems to work to neutralize the effects. I can only assume that it acts as a buffer to the oils in the nettle. I have 1st hand knowledge that it works.
I must be ammune to nettle iritation because I don't itch much when I go outside.
Well, that's why I specified an herbam based poison with EF9 dealing a mortal wound. I don't particularly care what it's called.
Acids and Akalines...
Jellyfish stings inject various kinds of toxins and nettles release a cocktail of skin irritants (histamines, acetylcholine, serotonine).
Funny that. I always thought that was a neurotransmitter in the brain. It's a skin irritant, too?
It's there to make sure you feel the rash. 
abe,
What do you think?
Oh, I see that you did. Sorry 'bout that!
I won't know until I can see the whole quote this was all that was printed,but saratone might stop the itchiness of poison ivy/nettles if it is apllied to the skin.
No.
You may try looking back at the original post that the quote came from.
I would suggest research into what Serotonin is, Abe. THEN you can start theorizing.
ser·o·to·nin
–noun Biochemistry.
a neurotransmitter, derived from tryptophan, that is involved in sleep, depression, memory, and other neurological processes.
serotonin
A monoamine substance that is formed from tryptophan and found in many animal tissues, including the intestine and central nervous system. In the brain, serotonin acts as a neurotransmitter that is involved in the control of pain perception, the sleep-wake cycle, and mood. Serotonin is also produced in some bacteria and plants.
As with the argument against Aluminium , Serotonin may not exist in Mythic Europe.
Disease is caused by Demons and malevolent plant fae cause the symptoms in this case.
Anyone with a modicum of skill in Philosophiae knows that the nettle sting is a sign of the presence of the fire principle in the plant. Proof is the redness of the skin and the burning sensation. 
All this talk of neurotoxins! I always forget things like that don't exist.
Maybe in Abe's version of Mythic Europe they do? Perhaps instead of science, all of history has been integrating magic, and researching it. Perhaps the ancient Greeks who created mathematics (and some science from it) were actually magi, and that all magi around the world can communicate with little devices called "Mobiles", which they can use to share information easily between themselves.
Perhaps, magic was created by God, when he created the world, and he sent down some angels to teach magi how to use it. Perhaps Abe's version got interfered with by demons, so it is hard for him to communicate his divinely inspired ideas.
Or perhaps Abe is just someone who needs to leave the library and make some friends.
(I know I spend too much time on the PC all day, I certainly need to get out and meet more people)