How much of G and H are you going to let one person buy? How do you make sure that the person is coming in to have bloodwork done if they're on D, E, and F? I

How much of G and H are you going to let one person buy? How do you make sure that the person is coming in to have bloodwork done if they're on D, E, and F? If a person is buying A over the counter and you prescribe B - where is that check being done?