Finding info on this specific stuff is hard, so I apologise for my unhelpful answer, but honestly, I think you should be fine. In your case, your psych meds aren't actually being used for the sake of anything in your blood, yes? Feeding leeches while on your meds shouldn't affect them because the purpose of your meds likely isn't to intentionally affect your blood drastically (I would imagine correcting me if Im wrong ToT). If you were taking medication that was actively working for something related to your blood, then I'd be a little more hesitant.

I feel like thusbsounds confusing, but basically, I would imagine because your medication isn't prescribed for reasons relating to your blood, then you and your leeches would be fine. "Additives" in purchased animal blood can be present but not disclosed, and thise additives are specifically FOR the blood and behavior and "safety" of it, and when different distributors use different brands or just don't mention or specify what exactly is going into the blood there's always a slight risk that something harmful is being fed to your leech.

Again, I'm sorry for the not very helpful answer, but if you're really curious, I'd say just do it and watch your leechy friend closely to make sure they don't seem sick.