How does Potion Toxicity work in The Witcher 2?

Solution 1:

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.

Solution 2:

As i found contradicting statements about what level of toxicity is needed to gain the effect of many talents in the alchemy tree i tested it out. I did 71 damage against an enemy creature. Then I learned the taster and the Metathesis talents (both 2/2) with should raise my damage about 40% while intoxicated. Drank a Swallow potion which in itself did not change my damage dealt. After that against the same enemy i hit for 100 damage, which is indeed about 40% more than 71. So:

with only one potion and toxicity level of 25 I got the benefits of the "while poisoned" talents!