IMO they know that better than 98% of the internet guys on the forum.Im going to give u the best advice u will probably use for doctor-patient relations that will work best for you & all of us who use these kinda supplements, & that is, NEVER SAY UR USING SUPPLEMENTS & DENY IT IF THEY ASK!!! Never tell a doc ur using any for of supplements such as creatine, ephedrine, test boosters, herbals, etc, because they will all say that they have negative effects, can do u harm, & they will be quick to blame whatevers wrong with u on the supps!!! I learned this a long time ago & have done this for years as ive been in the game for over a decade & am 35yrs old now.
On the other hand, (playing devils advocate), if ur having issues like high blood pressure, bad cholesterol, high liver enzymes, etc, & ur using ephedrine or test regularly, then u need to be smart enough to know the side effects of these supps & back the dosage down or take a break from it.
Oh & if u want a doc to confide in, then u need to find a sports/athletic doc like the ones used exclusively in pro sports. Only problem is that ur insurance may not cover it & they are expensive as hell!! At the age of 20 & with the fact that ur workin out to get bigger/stronger, i wouldn't go this route & would just stick to keepin quiet, make it known that u excersise alot, & that u lead a healthy lifestyle!! If anything just tell em u only take a multi vit, omegas, & d-3. Remember this as well, most doctors dont know much about sports supplements, so there confusion clouts there judgement.
If you want to ask them, ask them.