Although it initially seems kind of scummy, isn't this better than the majority of ad services anyway? In exchange for selling your medical data, you get a discount. It's essentially getting paid for sharing your data.

Of course if it's essential medication which people can't afford without the discount then that's another matter, but otherwise it seems kind of fair to me. And it gets a bit more complicated if you're in America where that data is going to be used by health insurance to adjust your premiums.