Clomifene, also known as clomiphene, is a medication used to treat infertility in women who do not ovulate, including those with polycystic ovary syndrome. Use results in a greater chance of twins. It is taken by mouth once a day, with a course of treatment that usually lasts for five days. Common side effects include pelvic pain and hot flashes. Other side effects can include changes in vision, vomiting, trouble sleeping, ovarian cancer, and seizures. It is not recommended in people with liver disease or abnormal vaginal bleeding of unknown cause or who are pregnant. Clomifene is in the selective estrogen receptor modulator (SERM) family of medication and is a nonsteroidal medication. It works by causing the release of GnRH by the hypothalamus, and subsequently gonadotropin from the anterior pituitary. Clomifene was approved for medical use in the United States in 1967. It is on the World Health Organization's List of Essential Medicines, under the category "Ovulation inducers" (Complementary List). Its introduction began the era of assisted reproductive technology. Clomifene (particularly the purified enclomiphene isomer) has also been found to have a powerful ability to boost or restore testosterone levels in hypogonadal men. Medical uses Ovulation induction Clomifene is one of several alternatives for ovulation induction in those who are infertile due to anovulation or oligoovulation. Evidence is lacking for the use of clomifene in those who are infertile without a known reason. In such cases, studies have observed a clinical pregnancy rate 5.6% per cycle with clomifene treatment vs. 1.3%–4.2% per cycle without treatment. Proper timing of the drug is important; it should be taken starting on about the fifth day of the cycle, and there should be frequent intercourse. The following procedures may be used to monitor induced cycles: Follicular monitoring with vaginal ultrasound, starting 4–6 days after the last pill. Serial transvaginal ultrasound can reveal the size and number of developing follicles. It can also provide presumptive evidence of ovulation such as the sudden collapse of the preovulatory follicle, and an increase in fluid volume in the rectouterine pouch. After ovulation, it may reveal signs of luteinization such as loss of clearly defined follicular margins and appearance of internal echoes. Serum estradiol levels, starting 4–6 days after the last pill Adequacy of LH surge by urine LH surge tests 3 to 4 days after last clomifene pill Post-coital test 1–3 days before ovulation to check whether there