At what point does it become medical blackmail?

A doctor prescribes, what he calls life saving medicine for high blood pressure, reminding you that it should be taken daily, without skipping a day, probably for the rest of your life.  Then that doctor refuses to renew the prescription until you come in and pay your $50 co-pay ever 6 months, just so he can re-check your blood pressure, which he already has you checking daily at home.  You’ve had the prescription for four years.  The doseage has never changed and the blood pressure is under control.  You can tell that the medicine is working by the fact that when you do not have the medicine the medicine to take your blood pressure rises to an unsafe (per the doctor’s numbers) level.

I do have respect for the medical profession in general.  Although I think most of the money spent on today’s medical pratices, could be better spent on medical research.  But that discussion is for another day.  I’m tried of doctors that help patient’s on a conditional basis.  If I feel bad I will go to the doctor. If he can help me, I’ll pay for his services.  If he milks me for preiodic payments, it’s medical blackmail.