I would've initially thought #2 because I know it can work that way with certain meds (I know the benzos and stimulants that I've tried specifically are like that for me), but I've had some scenarios with some meds (Ativan comes to mind) where I'll take 2mg of brand x and 2mg of brand y and have totally different reactions so #1 is a valid speculation as well.

There's also the "placebo/psychological" effect idea where maybe you think taking 2 pills is going to be more effective and therefore it is?? Possibly. Just throwing that as an idea out there. I might do that with antipsychotics (or they all just DO make me irritable and Rexulti DOES really make me compulsively chew myself...) (well, it does, but is that because that's a side effect or because I think it will so it does?)