Does poison go away over time or do I have to cure it?

Gah, spiders! I've just been poisoned by a big one. I do have the ingredients to make anti-venom, but I'm also in quite a safe place at the moment (well, apart from all the giant spiders).

Can I let my minotaur soak up the poison for a set time and then rest to regain the health, or do I have to use an anti-venom potion to cure him?

If you just walk it off, the poison will eventually go away on its own (or the character will die, which has the same net result :).

I've just done some tests with the spiders on level 3, with rather interesting results. At 8 points of poison resistance, I took an average of 84 HP of damage; with 58 points of poison resistance, I took an average of 35 HP of damage.

Some other notes:

1. Poison damage is dealt once every 8 seconds, more or less. It seems that with high poison resist, you will sometimes take 0 damage on a tick; if this happens, you won't see anything change.
2. At a constant level of poison resist, it seems to take a constant amount of time for the poison to clear out. For example, with 8 poison resistance, it consistently took 23 "poison ticks" in order to not be poisoned any more; if I put +50 poison resistance (58 total) bracers on my character, it consistently took 21 ticks for the poison to go away. However, this may just be because I took 0 damage twice and didn't notice. Hmm. This could be tested by measuring time elapsed, I guess.
3. The amount of damage you take per tick appears to be uniformly random; unfortunately, it doesn't go down over time :(
4. Saving after being poisoned and reloading will result in a different amount of damage being done to the character; the game is probably rolling dice per tick in the background :)
5. Adding poison resistance after being poisoned helps just as much as having poison resistance when poisoned - so if you've got one poisoned character, stack all your poison resist on them.

Here's my raw data if anyone wants to look at it. I noted where I think I took 0 points of damage with "0?".

In addition to the above answer, I noticed that if you sleep, you'll regain health faster than you lose it, so you can just wait it out and not end up with a dead character.