That last one is the one I use.
In my current game, drinking multiple potions requires a random* saving throw against DC 15 + (5 times number of previous potions imbibed in last 24 hours) for any past the first. So 20 for the second, 25 for the third, etc. Failure results in the having no effect and the imbiber becomes sickened for a number of minutes equal to the amount they failed the save by.
*This started as a Fortitude save but that skewed potion use towards warrior style characters since they tend to have higher fortitude which was never my intent. Now, some potions may make you dizzy (reflex), confused (will) or just sick (fortitude).