The person who wrote my letter is a counselor at my college's counseling center. And my doctor is technically a family practice doctor, though she sees a ton of trans people. The best way to go, though, is to find yourself a doctor who will prescribe T, whether that's your family doctor or not, and ask that doctor what he or she requires. Some doctors don't require a letter at all, some may have very specific specifications, and many will be somewhere in the middle.