I made one earlier without using Human Flesh, I'm pretty sure, yet the alchemy tool is only giving me results with Human Flesh as part of the recipe. I'm almost positive I made one earlier without it, was this before discovering a positive effect on a certain ingredient or are there other possible combinations?

I'm sorry if this has been asked before.

The alchemy table will only show the alchemy effects of ingredients IN YOUR INVENTORY. So you probably used the last one of that ingredient.

You have been eating your ingredients to find out their properties with the experimenter perk, right?

According to Darliandor's alchemy wizard, you have to use human flesh in that potion. Link: http://skyrim.melian.cc/?cmd=cmdSkyrim

I believe you need human flesh. The only ingredients I could find to create such an effect (a smart effect I might add) is imp stool with human flesh.