You are probably thinking of studies using 5 alpha-reductase inhibitors to increase the efficiency of androgen blockade in prostate cancer. While theoretically, finasteride would increase the efficiency of anti-androgens, thus reducing the effectiveness of strong androgens, I would think that Deca, having a stronger relative anabolic component to oxymetholone or tren, would not be affected and would be a better stack with Propecia. You might also ask Macro on this one. He seems to be well-versed in the latest biochemistry advances.