HCG

What it is

Human chorionic gonadotropin, or HCG, is a naturally occurring hormone made of two joined protein subunits, a structure chemists call a heterodimeric glycoprotein. One subunit is essentially identical to a piece shared by several other pituitary hormones, while the second, unique subunit gives HCG its own specific biological activity. The placenta makes it while a woman is pregnant, and the pharmaceutical version comes either from purifying it out of pregnant women's urine or from growing it in engineered cells.

HCG works by binding to and switching on the same receptor that luteinizing hormone, or LH, normally activates. In men that receptor sits on cells in the testes that produce testosterone; in women it sits on ovarian tissue involved in progesterone production and the final steps of egg maturation. This shared receptor is the basis for HCG's approved medical uses, which include supporting testosterone production, treating certain fertility conditions, and triggering final egg maturation during assisted reproduction.

How it is studied

HCG has the longest and most established research and clinical record among the compounds covered in this profile. It has been studied in randomized clinical trials and pooled analyses of those trials for its approved uses, including inducing sperm production in men with a hormone deficiency, correcting an undescended testicle in boys, and timing ovulation in fertility treatment, and separately in observational and off-label research looking at its role alongside testosterone therapy in adults. Because it has decades of approved medical use, much of the newer research looks at refining existing approved uses rather than establishing whether it works at all.

What studies report

• Pooling 41 studies of 1,673 men with a hormone deficiency that stops the testes working normally, gonadotropin treatment produced a measurable sperm count in most men after a median of 18 months, and combining HCG with a second hormone called FSH produced better sperm counts than HCG given alone. [muir-2025]
• Pooling 13 randomized trials in boys with an undescended testicle, hormone treatment with HCG successfully brought the testicle down in about 24 percent of cases, working mainly when both testicles were affected rather than just one; reported side effects were temporary and not severe. [bu-2016]
• In a meta-analysis of 13 studies on timing intrauterine insemination, a fertility procedure, using an HCG injection to trigger ovulation was not more likely to result in pregnancy than simply tracking the body's own natural surge of luteinizing hormone, suggesting HCG's established value in this setting is more about scheduling convenience than a higher chance of pregnancy on its own. [potapragada-2023]

What is not known

Its widely discussed off-label use alongside testosterone therapy to help maintain testicular function has less formal clinical trial support than its approved indications, and long-term outcomes from that specific off-label use have not been as thoroughly studied as its approved uses. Even within an approved use like inducing sperm production, achieving a sperm count high enough for a natural pregnancy is less common than simply achieving some measurable sperm count, and outcomes vary by the underlying cause of the hormone deficiency.

Regulatory status

HCG is approved by the United States Food and Drug Administration for specific indications, including certain causes of infertility, undescended testicles in children, and as part of assisted reproduction. Uses outside those approved indications, such as alongside testosterone therapy, are considered off-label. For most people, HCG is absent from the World Anti-Doping Agency's roster of banned substances, though male athletes face restrictions on it because of its effect on testosterone.