What is HCG?
HCG is a large hormone made of two protein chains with sugar groups attached. Its alpha chain is shared with LH, FSH and thyroid-stimulating hormone, while its beta chain is unique to HCG, which is why pregnancy tests look for the beta part. In pregnancy, HCG keeps the corpus luteum in the ovary making progesterone during the first weeks, until the placenta takes over that job.
Medical HCG has long been purified from the urine of pregnant women, and a recombinant version made in cell culture is also available. Because some tumors, such as certain testicular cancers, can produce HCG, it is also measured as a tumor marker. In fertility medicine, it is used to trigger the final maturation and release of eggs, and in men with low LH it is used to stimulate the testes.
How does HCG work?
HCG binds to the LH receptor, also called the LH/CG receptor, on cells in the testes and ovaries. In men, this receptor sits on Leydig cells, so HCG prompts the testes to make testosterone directly, bypassing the brain's own LH signal. In women, it supports the final steps of egg maturation, ovulation and progesterone production. HCG lasts considerably longer in the body than natural LH, which is part of why it became a standard LH substitute in medicine.
What has HCG research looked at?
- Ovulation and IVF
- HCG has been used for decades to trigger final egg maturation in fertility treatment, and it is one of the best studied hormones in reproductive medicine.
- Men with low LH and FSH
- In men whose pituitary does not make enough LH and FSH, HCG has long been used to raise testosterone, and combined with FSH or HMG to start sperm production.
- Men on testosterone therapy
- Small studies reported that adding HCG to testosterone therapy kept testosterone levels inside the testes higher, and some reports suggest it helps preserve sperm production. Larger controlled trials are limited.
- Undescended testes in boys
- HCG has been used for undescended testes, although current practice generally favors surgery.
- Weight loss
- The HCG diet, promoted since the 1950s, was tested in controlled trials that found no benefit beyond the very low calorie diet itself.
HCG has strong evidence behind its established fertility uses. Evidence for newer uses, such as alongside testosterone therapy, is real but smaller and comes mostly from modest studies. Its reputation as a weight-loss aid is not supported by controlled research.
HCG vs HMG and kisspeptin-10
These three act at different points in the same hormone chain. Kisspeptin-10 works at the top, in the brain, prompting release of GnRH, which then drives the pituitary to release LH and FSH. HCG skips the brain and pituitary and acts directly on the testes or ovaries, like LH. HMG also acts directly, but supplies both FSH and LH activity, and FSH is the main signal for sperm and egg development. Testosterone therapy, by contrast, quiets this whole chain.
HCG side effects and cautions
Reported side effects include headache, tiredness, irritability, fluid retention and pain where it is given. In men, HCG raises estrogen as well as testosterone, which can cause breast tenderness or growth. In women undergoing fertility treatment, the main serious risk is ovarian hyperstimulation syndrome, along with a higher chance of twins or more. Anyone with health questions about it should talk to a qualified clinician.
- Ovarian hyperstimulation
- In fertility treatment, HCG can trigger ovarian hyperstimulation syndrome, which ranges from bloating to serious fluid shifts and blood clots.
- Hormone-sensitive cancers
- Because it raises testosterone and estrogen, prostate cancer and other hormone-sensitive cancers are standard cautions.
- Early puberty
- In children, it can cause signs of early puberty.
- Pregnancy tests
- HCG will make a pregnancy test read positive for some time after it is given.
- Diet products
- Health agencies have warned against over-the-counter HCG weight-loss products, which have not been shown to work.
Further reading
This page summarizes the research in plain words. To read the studies yourself:
- Published studies on HCG PubMed, US National Library of Medicine
- Registered human trials of HCG ClinicalTrials.gov
