Is there any way to use poison on self / allies?

If the enemy uses poison, I presume it will heal me.

potion bottles with poison. Earth school spells which crate poison, poison barrels. Keep in mind that if you stand in puddles of poison, you can be set on fire more easily. (That's bad.)

Couldn't you also poison food and then eat the poisoned food.. I've never done the zombie thing, but it makes sense.

Poison is 100x easier to come across then "healing" items

Oh, and poison clouds.

Which can explode violently and leave a thick layer of smoke behind.

Where do I get poison from?

Any "Ooze Barrel" you come across = Infinite Poison source.

What i like to do is carry an Oil Barrel and an Ooze Barrel and drop them in the middle of the crafting space in town so you have everything you need in one spot.

Can I make poison potions using an Ooze barrel. What is the recipe?

...you take an empty potion bottle and drag it over the barrel. It's not rocket science.

Poison food JUST poisons you, it doesn't grant any additional healing or food buffs, so there's really no reason to use it over a poison potion.

I personally like to Zombie my whole party and then spam Poison Cloud arrows everywhere. They are ridiculously plentiful since they are made from just arrowheads, shafts, and an ooze barrel. The cloud then AoE heals my party while damaging any enemies that move through it, and if I need to heal faster I just move a bit because every step in poison heals me.

With that strategy I aim for Fire Resist ASAP so that when the clouds inevitably detonate it won't harm, and may even heal me further.