I think this could be a good add on to alchemy, to balance it though would mean you coul only mix one effect potions together, the other day I somehow while trying to find out ingrediants created a potion that caused targets magic regen to be 100% slower and to take away 50 points of something and then drain this for so long. This would not be mixable because of its multiple effects. I woul like to be able to mix of regen stamina potion and a add health to create that kind of potion, same with poisons. Or could the right combination create that anyway.

There are lot of combinations like that, oftentimes they have a positive and a negative effect together. Every once in a while I hit on something that has two positive (or negative effects) which is cool. They are all perfectly "mixable" if you have the required ingredients.

For one that gives you a bump to both regen stamina and health I assume you would need at least two ingredients that both provide those benefits and do not share a common negative effect. I don't know if that's one I've ever hit on by accident. I'm sure there is a list out there that gives all ingredients plus all four effects for each, but I haven't looked for it.

There's a perk at or near the top of the Alchemy perk tree called Purity that I'm pretty sure removes the possibility of potions having additonal negative effects and poisons having additional positive effects.

I get quite a few of the "two effect" mixtures because I like to experiment with ingredients, usually if it's a positive/negative combo the mixture just goes in the "stuff I'm gonna sell" category, the alchemy merchants seem perfectly happy to buy them.

My favorite positive/positive combo is the one that gives you equal amounts of Resist Fire and Resist Frost. Comes in real handy for fighting dragons, obviously, since you don't have to worry about figuring out whether the one you're fighting breathes one or the other or both.

In my second playthrough I actually hit on a three ingredient combo by accident that gave me equal amounts of Resist Fire, Resist Frost, and Resist Shock. And I'm pretty sure the bump for each was significantly higher than if you just mixed a Resist Magic potion. I jotted down the three ingredients somewhere but now I can't find it.

And a combination of certain potions would result in an explosion *cue fireball effect at alchemy table*

That resist fire + frost sound great, im gonna try to make it.

There is at least one ingredient that has both effects. Find that, and you're well on your way.