AAS use may also be associated with diminished libido and sexual functioning. This could be due to several factors. One is insufficient androgenic activity. This sometimes is noted with the use of primarily anabolic steroids such as methenolone, nandrolone, or oxandrolone, which may not provide sufficient androgenicity to compensate for suppressed endogenous testosterone. Studies also show that estrogen plays an important role in libido and sexual function in men. Therefore, the use of non-aromatizable steroids or aromatase-inhibiting drugs sometimes also causes interference. The addition or substitution of testosterone during a cycle is usually regarded as the most reliable way to correct issues with male sexual functioning, as it supplements the full spectrum of sex steroid activity. Note that sexual issues are also common after steroid discontinuance, when endogenous steroid levels are low.
Wlliam Llewellyn (2011) - Anabolics