If I drink a multiple effect potion of Fortify Light Armour, Fortify Sneak and Resist Poison

and then drink a multiple effect potion of Fortify Light Armour, Fortify Sneak and Invisibility

will the effects on Light Armour and Sneak stack and I will be Resistant to Poisons and Invisible, or will the second potion cancel the duplicate effects of the first potion?

Or what?

Cheers!

It depends on how the effects are set up. MGEFs that are set to Peak Value Modifier, and that have an "Assoc. Item #2" will not stack with one another, or with any other Peak Value Modifiers that share the same Assoc. Item #2. Another way to prevent stacking is to check the checkbox in the MGEF that says "Dispel Effects with these Keywords" and then include a keyword. http://www.creationkit.com/Talk:Magic_Effect#Peak_Value_Modifier

All other Magic Effects will stack. Usually this means Value Modifier type magic effects, or Peak Value Modifier effects without a second Associated Item.

Take a look at the magic effects that control each of those effects and you should be able to figure out the answer to your question.

Thanks for that. I was hoping there was an article somewhere.

I was not looking to prevent stacking, I just wanted to know what the game actually did. From that link it looks like I will have all four effects active, but the armour and sneak boost will be in a single dose?

I think one time I drank a potion of Enchanting 20% and Enchanting 30%, but I did not get a 50% boost to my Enchanting, IIRC.

Morrowind allowed some absurd abuse, so I suppose it's a good thing if Skyrim won't allow it.

Cheers!

Yeah, I know enchanting potions (and smithing/alchemy boost potions) do not stack. They are peak value modifiers that have a second associated item, so only the highest magnitude effect will stay active.