There is a myth being spread around both the net and the magazines today regarding which steroids are more likely to cause hair loss, but before we get to that, we must first gain an understanding of the subject of steroid “families”. Every AAS sold on the market today technically belongs to one of three classes (or families) of steroids. These are the testosterone-based, 19 nor-based, and DHT-based families of steroids. Each AAS is defined as belonging to one of these three classes of steroids, based on which of the three molecules it was originally derived from. For example, since the steroid Anavar is an alteration of the DHT molecule, it is classified as belonging o the DHT family of steroids. Since Dianabol is an alteration of the testosterone molecule, it is classified as belonging to the testosterone family of steroids. In reality, “all” steroids are derived from the testosterone molecule itself, but we utilize these 3 classes of AAS as basic sub-categories, in order to further categorize steroids into more specific groups.
I have heard several anecdotal reports of individuals who have stacked testosterone with Proscar (a 5-AR inhibitor) and have noticed significantly reduced performance enhancement effects. What’s going on here? We know it couldn’t be due to the inhibition of the direct anabolic activity of testosterone on muscle anabolism. Most likely it is due to the reduction of androgenic effects in other parts of the body that contribute to the ergogenic effects, specifically the CNS, which is stimulated by androgens to increase neural output leading to greater strength and greater recoverability. Another possibility is a reduction in the production of androgen dependent liver growth factors (such as IGF-1 ), since DHT is an important androgen in the liver.
DHT is a potent agonist of the AR, and is in fact the most potent known endogenous ligand of the receptor. It has an affinity (K d ) of to nM for the human AR, which is about 2- to 3-fold higher than that of testosterone (K d = to nM)  and 15–30 times higher than that of adrenal androgens .  In addition, the dissociation rate of DHT from the AR is 5-fold slower than that of testosterone.  The EC 50 of DHT for activation of the AR is nM, which is about 5-fold stronger than that of testosterone (EC 50 = nM).  In bioassays , DHT has been found to be - to 10-fold more potent than testosterone.