You know doctors and dentists make a big thing about privacy - they won't tell you anything about a patient unless that patient has signed a form saying they can release the information, and to whom.
Yet this kind of information gets leaked to telemarketers all the time. Some years ago I had borderline high blood sugar, and I started getting telemarketing calls from companies dealing in diabetic supplies. More recently I gave my phone number to another person's doctor, because she was having trouble keeping up with her appointments. One of her complaints is chronic pain, and now I'm getting telemarketing calls from companies dealing with that kind of ailment.
So it seems your best friend can't get the info without your permission, but the telemarketers are getting it without permission. I wonder who in the medical chain of people is getting paid to leak that information to the scumbags.