It’s not, actually!
Boldenone (EQ) doesn’t 5α-reduce to DHB
in vivo in man. [1]. It's part of the reason why I'm very careful to designate it by its name from the nomenclature, 1-Testosterone (1-Test; 1-Testo).
Boldenone singularly produces 5α-androst-1-ene-3,17-dione
in vivo in man, in only minuscule amounts since it is so resistant to 5α-reductase. [1].
I actually wrote about why boldenone (EQ) has these effects you're referring to here:
Understand the complex interaction of Primobolan and Equipoise with estrogen levels, symptoms of low estrogens, and practical decision-making strategies for managing these effects in AAS users.
thinksteroids.com
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References
[1] Goto, T., Tohkin, M., & Yamazoe, Y. (2019). Solving the interactions of steroidal ligands with CYP3A4 using a grid-base template system. Drug Metabolism and Pharmacokinetics. doi:10.1016/j.dmpk.2019.05.003