I'm not aware of any tests for Dopamine levels, but if they exist, nobody suggested testing. My PCP was the one who wrote me the prescription. He and I are neighbors and I see him and his family out while walking our dogs, so we're "connected" I guess you could say. Neither my Oncologist nor my Endocrinologist ever came up with any thoughts whatsoever about the origins of my fatigue and would just continually check my THS levels and they were ALWAYS perfect, the same every time. Apparently, they're not reading the literature because they've never heard about any of these other AE's. In fact, they didn't even know about Keytruda until I told them about it. Hard to believe really. I'm a Kaiser patient in N. CA, so that might tell you something.