I found this intresting PubMed summary that may shed some light on the reported benefits of 4OH-T. DmitryWI, and others, have repoted this compound to reduce sides when added to stacks. It would appear that this is related to DHT antagonism. It not only acts as an AI, but improves DHT related sides not by 5-reductase inhibition, but by AR competetive inhibition due to strong receptor affinity. It makes sense why this is a good addition to stacks that generate undesirable metabolites. It also points to why 4OHA and 4OHT support libido:
J Enzyme Inhib. 1992;6(2):141-7.
Effects of 4-hydroxyandrost-4-ene-3,17-dione and its metabolites on 5 alpha-reductase activity and the androgen receptor.
Davies JH, Shearer RJ, Rowlands MG, Poon GK, Houghton J, Jarman M, Dowsett M.
Department of Urology, St. Georges Hospital, London, England, UK.
The steroidal aromatase inhibitor, 4-hydroxyandrost-4-ene-3,17-dione (4OHA) and its metabolites, 4-hydroxytestosterone (4OHT), 3 beta,17-dihydroxy-5 alpha-androstan-4-one (metabolite A) and 3 alpha, 17-dihydroxy-5 beta-androstan-4-one (metabolite B) were evaluated as inhibitors of the human prostatic 5 alpha-reductase enzyme and for binding to the rat prostatic androgen receptor. 4OHA and 4OHT were weak inhibitors of 5 alpha-reductase with IC50 values of 15-29 microM. Metabolites A and B had no significant inhibitory activity. 4OHA and metabolites A and B bound weakly to the androgen receptor. The binding affinities (RBA) relative to mibolerone (RBA = 100) were 0.085, 0.485 and 0.016, respectively. However, 4OHT (RBA = 75) was a more potent binder than the endogenous androgen 5 alpha-dihydrotestosterone (RBA = 66). The ability of these metabolites, in particular 4OHT, to bind to the androgen receptor may explain the in vivo androgenic activity of 4OHA.
PMID: 1284430 [PubMed - indexed for MEDLINE]