The sleeve is working for me with the medication I take - Wellbutrin SR, I initially took IR right after surgery. I have trouble w IR - as it dumps too quickly and then I am in a crying puddle on the floor, and in an altered surgical besides, hmm - it wasn't pretty.
It would be a logical conclusion that in the bypass because the small intestine is bypassed that medications/nutrients have less chance to absorb or breakdown, as that is exactly how that surgery is designed to work. Dosage and finding the 'right' psychiatric drugs are difficult in the first place, let alone considering malabsorption along with it.
Good luck on your journey.
