I was taking it every so often for a while and pretty much always regretted it, so it's pretty much on my shit list now. It's a really shittily explained and mechanical item, and very rarely does it ever turn out in your favor. All Experimental Treatment does is raise or lower each of the stats it affects (which I think is almost everything, including heart containers, but exempting Luck) by a random amount within a - to + range, dependent on each stat. That description has always been a straight up lie. The thing is, Experimental Treatment does not, nor has it ever, shuffled the stats after the change. I don't believe that's true, 2 pips for Isaac would be the same amount of damage as 2 pips for Cain (except that '2 pips' has a range associated with it regardless.) Where say, 2 in damage is actually 3.0, but 2 in tears is 2.0, and if you swap the raw values, damage becomes 1 pip + invisible fraction, and tears becomes 3 pips.
2 pips of damage for Isaac is a different actual amount of damage than 2 pips for Cain, so I was guess that a similar scheme is going on between each stat.
They aren't based on the character as far as I know.
