Pharmaceutical hCG is obtained from two sources; it can be isolated from the urine of pregnant women or produced by recombinant technology – similar to the production of human growth hormone.20 hCG is normally produced in trace amounts in humans, except for during the state of pregnancy. The fetus (unborn baby) is attached to the wall of the mother’s uterus by a flat, plate-like appearing gland called the placenta; sometimes it is referred to as the afterbirth as it is expelled immediately after the baby is born. The placenta is extremely vascular; meaning a highly concentrated network of blood vessels is present in the tissue. It serves several functions, including bringing nourishment to the fetus from the mother’s blood, eliminating fetal waste into the mother’s blood, protecting the fetus from exposure to many but not all drugs and infectious agents (viruses, bacteria, etc) and lastly producing many hormones that support the state of pregnancy. Among the hormones produced, the most prominent is hCG.21 hCG is a glycoprotein hormone and is easily detectable in the urine, making it the basis for home pregnancy test.

    In men, the testicles are directly stimulated to produce testosterone by a hormone released from the pituitary gland called luteinizing hormone (LH). hCG is structurally very similar to LH with a few differences that make it more stable and longer-acting.22 This is critical as during pregnancy the placenta must maintain the uterus for nine months between menstrual periods, instead of the usual 28 days.

    LH is released in a roller-coaster pattern of spikes and valleys and its effect is short-lived, causing testosterone to be released in several bursts throughout the day.23 hCG’s effect is longer acting, allowing it to be dosed just once a day or even every other day. When hCG is given to a man with normally functioning testicles, the longer acting signal results in dose-dependent elevations in testosterone concentrations; meaning that higher doses result in greater elevations in testosterone, to a point.