|Systematic (IUPAC) name|
|Pregnancy cat.||B3 (Au), X (U.S.)|
|Legal status||S4 (Au), POM (UK), ℞-only (U.S.)|
|Metabolism||Hepatic (with enterohepatic circulation)|
|Excretion||Mainly renal, some biliary|
|Mol. mass||406 or 598.10 (with citrate)|
| (what is this?)
Clomifene (INN) or clomiphene (USAN) (trademarked as Clomid and Omifin) is a selective estrogen receptor modulator (SERM) that increases production of gonadotropins by inhibiting negative feedback on the hypothalamus. This synthetic drug comes supplied as white, round tablets in 50 mg strength only. It has become the most widely prescribed of all fertility drugs. It is used in the form of its citrate to induce ovulation. It is used mainly in female infertility, in turn mainly as ovulation induction to reverse oligoovulation or anovulation such as in infertility in polycystic ovary syndrome, as well as being used for ovarian hyperstimulation, such as part of an in vitro fertilization procedure.
Mode of action 
Clomifene inhibits estrogen receptors in hypothalamus, inhibiting negative feedback of estrogen on gonadotropin release, leading to up-regulation of the hypothalamic–pituitary–adrenal axis. Zuclomifene, a more active isomer, stays bound for long periods of time.
In normal physiologic female hormonal cycling, at 7 days past ovulation, high levels of estrogen and progesterone produced from the corpus luteum inhibit GnRH, FSH and LH at the hypothalamus and anterior pituitary. If fertilization does not occur in the post-ovulation period the corpus luteum disintegrates due to a lack of beta-hCG. This would normally be produced by the embryo in the effort of maintaining progesterone and estrogen levels during pregnancy.
Therapeutically, clomifene is given early in the menstrual cycle. It is typically prescribed beginning on day 5 and continuing for 5 days. By that time, FSH level is rising steadily, causing development of a few follicles. Follicles in turn produce the estrogen, which circulates in serum. In the presence of clomifene, the body perceives a low level of estrogen, similar to day 22 in the previous cycle. Since estrogen can no longer effectively exert negative feedback on the hypothalamus, GnRH secretion becomes more rapidly pulsatile, which results in increased pituitary gonadotropin (FSH, LH) release. (It should be noted that more rapid, lower amplitude pulses of GnRH lead to increased LH/FSH secretion, while more irregular, larger amplitude pulses of GnRH leads to a decrease in the ratio of LH/FSH.) Increased FSH level causes growth of more ovarian follicles, and subsequently rupture of follicles resulting in ovulation. Ovulation occurs most often 6-7 days after a course of clomifene.
Clomifene is a mixture of two geometric isomers, enclomifene (E-clomifene) and zuclomifene (Z-clomifene).
Adverse effects 
Common adverse drug reactions associated with the use of clomifene (≥1% of patients) include: vasomotor flushes (or hot flashes), abdominal discomfort, visual blurring (dose-dependent), and/or reversible ovarian enlargement and cyst formation. Infrequent adverse effects (0.1–1% of patients) include: abnormal uterine bleeding, nausea, and/or vomiting. Rare adverse effects (<0.1% of patients) include: reversible alopecia and/or ovarian hyperstimulation syndrome.
In comparison to treatment with purified FSH, the rate of ovarian hyperstimulation syndrome is low when using clomifene.
Clomifene can lead to multiple ovulation, hence increasing the chance of twins (10% of births instead of the normal ~1%) and triplets; some parents-to-be then opt for selective reduction to reduce the number of fetuses.
Off-label use in the treatment of male hypogonadism 
Clomifene citrate has been found very effective in the treatment of secondary male hypogonadism in many cases. This has shown to be a much more attractive option than testosterone replacement therapy (TRT) in many cases because of the reduced cost and convenience of taking a pill as opposed to testosterone injections or gels. Unlike traditional TRT it also does not shrink the testes and as a result can enhance fertility. Traditional TRT has the risk of inducing a chemical gonadectomy, although with monitoring and low-dose hCG as adjunct, this is usually preventable and reversible. Because clomifene citrate has not been FDA approved for use in males it is prescribed off-label. Due to the fact that Clomifene is now a generic medication in most markets, it is unlikely that a drug company would pursue FDA approval for use in men now because of limited profit incentive, mostly due to the relatively small market potential. However, the single isomer of clomifene, enclomiphene under the brand name Androxal, is currently under phase 2 trials for use in men.
Prohibited use in sports and use in bodybuilding 
Clomifene is commonly used by male users to bind the estrogen receptors in their bodies, thereby blocking the effects of estrogen, such as gynecomastia. It also restores the body's natural production of testosterone. . It is included on the World Anti-Doping Agency list of illegal doping agents in sport.
Clomifene has been used since the 1960s. It was first used to treat cases of oligomenorrhea. When it was realized that women undergoing treatment had higher than expected pregnancy rates, it was then applied to treatment of anovulation.
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- How Clomid Works in Men
- Androxal website
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