Power
You will have the power to prescribe pills. We need thyroid hormones to survive, and considering that many of your clientele may have issues with their thyroid or have had their thyroid glands removed because of cancer, then it seems that you hold the balance of their lives in the palm of your hand. That's some serious stuff.
You can also balance blood sugar with a single RX, and control whether or not a kid grows up with a Napoleon complex by not growing at all.