Friend is tinkering with meds how do I find out for sure?

This is so vague, what you have written. I would suggest that like me this fellow find a doctor that has a practice at the clinic that has a "My Chart" this is an online communicationwith your doctor. I can ask my doc, for instanc eif I am dieting, to try out lower doeses of my diabetic med. I stay in touch with him or his nurse on line. Maybe something like that would help. I suppose however if this person is secrative you could just give him some base line observances and add if your blood sugar is a (certain number) it seem s your showing these symptoms. Then lets say lets check your number?