Clomiphene citrate is a drug given to women for use as a fertility aid. It is a SERM (Selective Estrogen Receptor Modulator) which acts by actually binding to the estrogen receptor and thereby blocking estrogen from doing the same. Clearly, this is advantageous when it binds to breast tissue, and prevents estrogen from binding there to cause gynocomastia (although it is not nearly as effective as nolvadex for this purpose). It also opposes the negative feedback loop that the body has with regards to estrogen and the HPTA (Hypothalamic-Pituitary-Testicular-Axis), and this in turn stimulates LH (Leutenizing Hormone) and FSH (Follicle Stimulating Hormone). LH and FSH, in turn stimulate the release of testosterone. Clearly this is advantageous to bodybuilders and athletes coming off of a cycle, and beginning their post-cycle-therapy. What we have in Clomid is essentially a drug that acts as a preventative measure against gynocomastia, as well as a drug that acts to raise endogenous (natural) testosterone levels. Usually, it is compared with another SERM, Nolvadex, for those reasons.
Clomid, however, is much weaker than nolvadex in a mg for mg comparison, with roughly 150mgs of clomid being equal to 20mgs of nolvadex (1).It should be noted, however, that 150mgs of clomid will still raise testosterone levels to approximately 150% of baseline value(1). You don't have to use 150mgs, however; in my research, Ive found that doses as low as 50mgs will show improvements and elevations in testosterone levels (4). In fact, my original Post-Cycle-Therapy regime (as suggested by Dan Duchaine in the original Underground Steroid Handbook) was 100mgs per day for a week and 50mgs/day for a week. Dont laugh& for the late 90s, when most anabolic steroid users didn't even know how to use Clomid, it was considered a "state of the art" PCT routine. I suspect that Duchaine originally introduced this compound to the steroid using community.
Clomid, just like nolvadex, is very safe for long term treatment of lowered testosterone levels (2), with some studies showing its safety and efficacy for up to four months. And post-cycle, when steroid users are suffering form lowered testosterone levels, is when clomid is most effective.