Like other AAS, drostanolone is an agonist of the androgen receptor (AR).  It is not a substrate for 5α-reductase and is a poor substrate for 3α-hydroxysteroid dehydrogenase (3α-HSD), and therefore shows a high ratio of anabolic to androgenic activity.  As a DHT derivative, drostanolone is not a substrate for aromatase and hence cannot be aromatized into estrogenic metabolites .  While no data are available on the progestogenic activity of drostanolone, it is thought to have low or no such activity similarly to other DHT derivatives.  Since the drug is not 17α-alkylated , it is not known to cause hepatotoxicity . 
Since estrogen offers us no trouble, side effects are generally mild with this steroid. As discussed earlier, gynecomastia and water retention go unseen. So are problems controlling blood pressure, again usually associated with estrogen. Masteron is also not liver toxic, so there is little concern stress will be placed on this organ, even during longer cycles. The only prominent side effects stem from the basic androgenic properties of dihydrotestosterone. This includes oily skin, acne, body/facial hair growth, aggression and accelerated hair loss. Since this compound is already a synthetic DHT, Proscar would have no impact on the level of androgenic effects. Men with a receding hairline (or those with a known familial predisposition for baldness) may therefore wish to stay away from Masteron completely, as the potent androgenic effect of this steroid can easily exacerbate such a condition.
Some bodybuilders and athletes use trenbolone esters for their muscle-building and otherwise performance-enhancing effects.  Such use is illegal in the United States and many other countries. The DEA classifies trenbolone and its esters as Schedule III controlled substances under the Controlled Substances Act .  Trenbolone is classified as a Schedule 4 drug in Canada  and a class C drug with no penalty for personal use or possession in the United Kingdom .  Use or possession of steroids without a prescription is a crime in Australia .