Being intoxicated is not like in The Witcher, where you used to start shaking and lose control of Geralt.
Here, intoxication level only limits the amount of potions you can pour down.
Some talents allow you, so to speak, to "spread this poison" to your enemies.
They are the type "+xx to yyy .. while intoxicated"
Excerpt from an interview with Tomasz Gop:
WV: How many potions can Geralt drink in one sitting? Assuming zero alchemy skills and minimal toxicity of each of the potions? How does the overdose look in Witcher 2?
Tomasz Gop: Well, you have to understand that right now, drinking potions is done during meditation only. You have a projected level of toxicity shown in a bar when adding potions to the batch you're going to drink before leaving meditation. This level cannot be exceeded.
WV: Hang on, what about the overdose then? We've heard about a possibility to overdose potions -- unlike in Witcher 1, it was supposed to be something akin to actual poisoning, whereby Geralt starts shaking uncontrollably and you lose control of your character for a while...
Tomasz Gop: Unfortunately, there's no overdose this time. It's not that we had to cut out this part, we just didn't have time to add that feature.