Trenbolone has near zero progestational activity, as found both in veterinary science and in cell studies. Its activation of the progesterone receptor (PR) is about 100 times weaker than that of progesterone itself. Trenbolone Acetate Revalor levels achieved during steroid cycles cannot activate the PR to even a small fraction as much as is caused by natural progesterone levels.
At least one veterinary study also found Trenbolone Acetate to not increase prolactin measurably, despite depressing thyroid levels.
In your friend’s cycle, prolactin may well have increased. Where an aromatizing steroid is used and estrogen levels are not controlled with an anti-aromatase, estradiol levels typically rise. This often but not always causes an increase in prolactin, and sometimes a large increase.
It’s impossible to determine why gynecomastia developed for your friend this time but not on the previous occasion, particularly as no blood test was performed. Uncontrolled increase in estrogen due would certainly have contributed. Elevated prolactin caused by increased estrogen could be a contributor.
Authentic Trenbolone Acetate Revalor actually works against estrogenic differentiation of the mammary gland, or at least this has been found in veterinary science.
It can be difficult to attribute cause when gyno occurs during trenbolone cycles. Sometimes, as in this cycle, other causes could completely explain it. In others, the trenbolone product seems the only possible cause.
When veterinary and pharmaceutical preparations were the only sources of trenbolone, gyno was never attributed to this steroid. It also appears never to occur when trenbolone is personally prepared from Finaplix H (not S.) For this reason, I doubt that authentic trenbolone can cause gyno.
However, underground preparations sold as Trenbolone Enanthate have promoted gyno in many cases. Whether this is due to substitution, oxidation of the material, or some other reason is unknown to me. I’d advise personally preparing from powder, having verified that the powder is moderately yellow, not brown, and is strongly spicy to the taste. This will at least make it highly likely that the product contains trenbolone. Another alternative is to prepare personally from Finaplix H. Doing so allows absolute certainty.