Except for Rutnin, where I had two cataracts removed, I use my nearest hospital for diabetes testing and medicine (pills are paid for by my corporate health insurance). As others mention, there seems to be a thing in Thailand about selling pills at inflated prices for everything.
Can't complain about the quality of doctors. When my prostate ballooned, I went to my local hospital and a famous 5 star hospital in town for a second opinion. Both said the same thing, which gives some confidence that I'm not going to pop off soon.
More worrying was that I used to know a young man who was doing his medical degree. He could never answer my enthusiastic questions about his studies, telling me, "I took that exam last month and can't remember now."