Trenbolone and Cortisol
While the mass gain results from trenbolone can instead be achieved with high milligram amounts of other injectable anabolic steroids, trenbolone differs from them in being stronger as a glucocorticoid (cortisol) antagonist and in decreasing blood corticosteroid levels. For this reason, it reduces subcutaneous water retention. And further, this anti-cortisol effect can make a significant difference in fat loss. It may also be a partial explanation for any increased tendency to aggression that is sometimes seen with trenbolone.
Trenbolone and Progestagenic Activity?
With regard to activity at other receptors, many have written regarding theories of progestagenic activity of trenbolone. Where legitimate trenbolone is used, practical experience shows no detectable effect with regard to water retention or gynecomastia. Veterinary literature reports no detectable progestagenic effect. And if this were not enough, recent cell culture research shows progestagenic potency to be only about 1% that of progesterone itself, which would not be an important amount.
For these reasons, I would make no decisions against trenbolone from fears of claimed progestagenic activity. It is a very well-proven compound in bodybuilding, including in contest-prep situations where an actually-progestagenic compound would be very unsuited.