Extreme potions, according to the Tip.it guide, require a three-dose potion and the secondary. Does it work if you use a four-dose potion? If not, is there a way of easily getting three-dose potions without losing out on a quarter of it? I didn't particularly read the update info when it was released as I wasn't high enough level to be able to utilise it properly.

If you want to change your 4 dose potions into 3, go to east of nardah bank and there is a person that decants at the cost of extra vials.