Thats not always true. The Dr. needs to know if you've been using "substances" to make the right evaluation of treatment, even if you don't just blurt out and say it, you need to atleast hint around till he gets the point. I find it's allot like talking to a lawyer.
I told my doctor about the truth about my AAS use and have since gotten a great life insurance policy for myself. You just have to ask your doctor not to go writing it in your medical record. They are more then happy to do so if you ask.
I'm a pilot and would lose my wings if the doctor wrote anything about them in my medical chart that would disqualify me from renewing my Medical Certificate every couple of years.
It may help to dance around the question by telling him that you use supplements and other bodybuilding aids that could be the reason for your hormone problems. Just don't be so sure about what they are called or the legality of them.
Once you feel comfortable with the doctor, you may change your mind as I did and be honest about the AAS.