The way I see it, it just turned a relatively safe--if somewhat dull--stalemate into a situation that risks spilling the cauldron and getting everyone there splashed to the point that they have no idea what they're doing there (if the dosage even lets them retain such things as a general sense of self, language, or how to walk).
I thought that, because it's a "poison", it only has an effect if ingested or inhaled. But it seems D&D uses the word for contact-toxic substances too.
I thought poison was any toxin that did not require the skin to be damaged. (so ingested poisons, inhaled poison, contact poisons) As opposed to a venom, which does require puncturing the skin.
Outside of D&D? Biologically, it's any substance that causes death, injury, or harm to organs, tissues, cells or DNA. Medically and zoologically, differentiation is a bit more finely-tuned. Toxins are harmful substances specifically produced by biological means, though definitions can be lax. Venoms are animal poisons specifically delivered subcutaneously (hence not including poison dart frogs, which are absorbed through skin but not injected). Poisons are sometimes not included in the previous two rather than being a superset and thus serve as a category of the excluded, in which case "toxicant" is used as a supercategory for any toxic substance. On the adjective side, venom
ous animals are those that deliver venom via such means, while poisonous animals deliver either a toxin (if they produce it themselves or obtain it from other living things, as do poison dart frogs) or a poison (if they store it from non-organic sources, for which I don't have an example off-hand). Venomous and poisonous tend to be considered mutually exclusive, and as noted, this occurs with venom and poison on occasion as well.
So, for example, a snake's venom is also a toxin and a poison, but it is not considered poisonous (despite the fact that consuming its venom glands directly will give most people a bad time). As noted in an aside, poison-dart frogs are poisonous, but not venomous. Arsenic is a poison that is highly toxic, but it is not a toxin unless you're in a context where people refer to such things as inorganic or environmental toxins.
Behold the joys of multiple fields that have developed their own very specific meanings and their own very specific pedants. We're the Internet; we have entire forests of pedantries.