This double bond attribute of Equipoise makes it difficult to bind with the androgen receptor producing a much lesser anabolic effects as the other steroid.
Equipoise can cause several side effects to men such as low testosterone production, erectile dysfunction, problems in spermatogenesis and decreased libido.
Source:
Equipoise Steroid Profiles | Steroids
I was able to find some evidence online which suggests equipoise may decrease libido. I learned equipoise was originally created to be an injectable form of dianabol.
I found some cool info about the action of testosterone on androgen receptors.
The pharmacodynamic action of anabolic steroids begin when the exogenous hormone penetrates the membrane of the target cell and binds to an androgen receptor located in the cytoplasm of that cell. From there, the compound hormone-receptor diffuses into the nucleus, where it either alters the expression of genes[20] or activates processes that send signals to other parts of the cell.[21] Different types of anabolic steroids bind to the androgen receptor with different affinities, depending on their chemical structure.[3] Some anabolic steroids such as methandrostenolone bind weakly to this receptor in vitro, but still exhibit androgenic effects in vivo. The reason for this discrepancy is not known.[22] On the other hand, steroids such as oxandrolone bind tightly to the receptor and act mostly on gene expression.
Source:Wikipedia
I can't seem to find anything that tells me how equipoise binding to the androgen receptor releases a chemical causing reduced libido.