How do decoctions work?

I remember hearing about decoctions for the first time in a preview video, I wasn't impressed back then. But I think I might have misunderstood some aspects, so I'm looking for some clarifications on the mechanics of decoction use.

• Are they single-use only, or are they refilled like regular potions?
• What does the +100% toxicity effect mean exactly?
• Can I have multiple decoctions active at the same time?

I experimented a bit myself with decoctions, and found the following about the mechanics of them.

They do replenish like potions do, as already stated in another answer. They also have vastly greater durations at around 30 minutes. But the way toxicity works is fundamentally different than with potions. The toxicity from decoctions doesn't seem to decay, it was set to a fixed 80/100 in my case (without any skills in the alchemy tree).

This means that it is impossible to have two decoctions active at once as it would exceed the maximum toxicity value. It also means that while using some potions is still possible in addition to a decoction, it is severely limited. In my case, only potions with 20 toxicity can be used, as that is all that is left to the maximum of 100. And each potion use did cause a signficant health loss as I hit the maximum toxicity value.

The +100% Toxicity rule simply means that each additional potion counts for double. While a decoction is working, the effects of other potions will stack more quickly.

If you look at the first tier of the Alchemy skill tree, however, Acquired Tolerance is a very powerful way to increase your maximum Toxicity. Every new formula you learn increases this value... and those points add up quickly.

I'm lv.14 right now, and my maximum Toxicity has cleared 200... Though I haven't tried it yet, I think I have enough room that I could possibly run a second decoction at the same time. I can certainly say that, at this point, there is almost no practical limitation on how many potions I can use in a single fight.

• They can be replenished when you meditate just like potions

• The +100% Toxicity appears to be meaningless, as of 1.05 on PC. Decoctions use up 70 (basilisk uses 40) of your max toxicity while they are active. It's important to note that this won't activate the Killing Spree or Frenzy abilities, as they are specific to POTION toxicity. Having 2 or even 3 decoctions active at once is possible, and Tissue Transmutation give a bonus for each. Decoctions do NOT increase the toxicity burden of potions.

• Max toxicity is at least 277 with all the abilities and all the recipes I know about in the base game. If it's higher, it isn't much and it certainly isn't another 43. So, you could have 3 decoctions active at once. You wouldn't have much "room" for potions though.

  • As of the release of Blood and Wine, max toxicity is around 345 with the correct skills and gear, allowing for a maximum of 4 non-Basilisk decoctions, while leaving 65 toxicity for potions or Basilisk.