Reproductive axis (HPG)

Enclomiphene is the trans isomer of clomiphene, the fertility pill, taken on its own without the longer-lasting cis isomer zuclomiphene. By blocking oestrogen feedback on the brain, it raises LH and FSH and so the body's own testosterone. In phase 2 and 3 trials in men with secondary hypogonadism, 12.5–25 mg a day raised testosterone about as much as testosterone gel while keeping sperm counts normal, which the gel did not. Regulators in the US and Europe declined to approve it, and development stopped in 2021.

Human chorionic gonadotropin (hCG) is a placental hormone that acts as a long-lasting stand-in for luteinising hormone (LH), the pituitary signal that tells the testes to make testosterone. It has been used for decades to start puberty and sperm production in men whose pituitary makes too little LH and FSH, and to trigger ovulation in IVF. Low doses keep testosterone inside the testes near normal while men take testosterone. As a weight-loss injection, it does no better than placebo.

Human menopausal gonadotropin (hMG, menotropins) is a mixture of FSH and LH activity purified from the urine of postmenopausal women. Its main use is stimulating the ovaries for IVF, where a 2026 Cochrane review of 59 trials found slightly more live births and less ovarian hyperstimulation than with recombinant FSH. In men whose pituitary makes too little LH and FSH, it is added to hcg to start sperm production when hCG alone is not enough.

Kisspeptin-10 is the shortest natural form of kisspeptin, the hypothalamic hormone that switches on the reproductive axis. It is the ten amino acids at the end of the longer kisspeptins and keeps their full activity at the kisspeptin receptor. A single injection releases GnRH and so LH within minutes, and infusions raise testosterone in healthy men and in men with type 2 diabetes and low testosterone. It clears from the blood in about 4 minutes, so studies have used infusions, and its effects in women depend on the phase of the menstrual cycle. It is not approved for any use.