I don't think any single affect that cripples you and is nearly uncurable should last more than 30 ticks at the outside. 20 seems like plenty to me.

I've never played a poisoner/trapper nor am likely to ever play one, but I think that poison immunity is too strong against poisoners. My suggestions would to make poison immunity act like poison resistance against thief poisons, and only confer true immunity to poison damage and basic poison.

However, I don't think neurological poison needs to be nerfed in its effects. It is a very strong ability, but it's about on par with something like forget or deafen. It's a death sentence for non-melee classes if they can't get away, but mostly just causes people to flee/quaff. And it's not like poisoners really have a lot of power otherwise. Sure, when combined with stealing and long knockouts it's extra nasty, but a worn container with a potion in it will solve that problem. Unless you're also blinded, but at that point so what if it is a death sentence?

Just to throw out a wild idea, I'd like to see the poison path rebalanced (in terms of cost and effects) around not having to regather ingredients constantly. They should still be necessary, but have 10-20 charges per ingredient. The current grind/time-sink dynamic makes things fair balance-wise, it's just incredibly anti-fun. If the main thief paths were just thug, binder and city ties, and trappers and poisoners were nerfed to be expensive adjunct paths, that would be a better design it seems to me. I'm making a pretty big assumption that the current way traps/poisons work is that the ingredients are consumed every time. If that's already not true, well then ignore this (and maybe I'll try a poisoner sometime).