HCG with TRT: What It Does for Testosterone, the Testes and Fertility
Hormonal, Growth Hormone & Body Composition Research
Why add HCG to testosterone therapy? Because three weeks of TRT on its own cut the testosterone inside healthy men’s testes by 94%. In the men who also received HCG at the highest dose tested, it finished 26% above where it started. That 2005 result, and a 2013 study in which none of 26 men on TRT plus HCG became azoospermic, form the core of the published case for HCG alongside testosterone. Here is what both studies did, what the men received, and what changed.
View product →Findings
- Testosterone therapy switches off the pituitary signals that drive the testes. In a 2005 trial, LH and FSH fell to 5% and 3% of baseline and testosterone inside the testes fell 94% in three weeks.
- Adding HCG restored testicular testosterone in step with the dose: 25% below baseline at 125 IU, 7% below at 250 IU and 26% above at 500 IU, each given every other day.
- In a 2013 Journal of Urology study of 26 men on TRT plus HCG, no man became azoospermic and semen measures did not change during follow-up.
- 9 of the 26 men contributed to a pregnancy with their partner during the study.
- About 80% of testicular volume is sperm-producing tissue, which is why the testes shrink when that tissue loses its hormonal signal (Patel et al., 2019).
Why testosterone therapy shrinks the testes
The testes run on two signals from the pituitary gland. Luteinising hormone (LH) tells the Leydig cells to make testosterone, and follicle-stimulating hormone (FSH) works with that testosterone to drive sperm production. When testosterone arrives from outside the body, the brain reads the higher level and turns both signals down. The result is a paradox: testosterone in the blood goes up, while testosterone inside the testes goes down.
That inner level is the number that matters. In the 2005 trial below, the men’s blood testosterone at baseline was just 1.2% of the level measured inside their testes. Sperm production depends on that high local concentration, and roughly 80% of testicular volume is the tubules and germ-cell tissue where sperm are made. When the signal goes, that tissue slows, and a 2019 review in the World Journal of Men’s Health notes that this usually shows up as testicular atrophy. The 2013 study’s authors open their paper with the same point: testosterone therapy lowers LH, FSH and testicular testosterone, impairs sperm production, and leads to azoospermia (no sperm in the ejaculate) in 40% of patients.
The 2005 trial: measuring testosterone inside the testes
A team led from the University of Washington in Seattle set out to find how much HCG it takes to keep testicular testosterone in range while testosterone therapy suppresses LH. They randomised 29 healthy men to 200 mg of testosterone enanthate a week, combined with either a saline placebo or HCG at 125, 250 or 500 IU every other day, for three weeks. Testosterone inside the testes was measured directly, in testicular fluid drawn by fine-needle aspiration at the start and at the end. The results appeared in the Journal of Clinical Endocrinology and Metabolism in 2005.
| Group, three weeks | Testosterone inside the testes, against baseline |
|---|---|
| Testosterone + placebo | 94% lower (1,234 to 72 nmol/L) |
| Testosterone + HCG 125 IU every other day | 25% lower |
| Testosterone + HCG 250 IU every other day | 7% lower |
| Testosterone + HCG 500 IU every other day | 26% higher |
In the placebo group, LH and FSH fell to 5% and 3% of their starting levels. Across the HCG groups, testicular testosterone rose in a straight line with the dose (P<0.001). The authors concluded that relatively low-dose HCG maintains testicular testosterone within the normal range in healthy men whose LH and FSH are suppressed.
The 2013 study: 26 men on TRT and HCG
The 2005 trial measured hormones. The question men on TRT actually ask is about sperm, and that is what a 2013 study in The Journal of Urology answered. Hsieh, Pastuszak, Hwang and Lipshultz reviewed the records of 26 men with low testosterone, mean age 35.9, who were on testosterone therapy together with low-dose HCG. Nineteen used weekly testosterone injections and seven used a daily gel. The men in this study received 500 IU of HCG by intramuscular injection every other day alongside their testosterone, and were followed for a mean of 6.2 months.
- Testosterone rose as intended: mean blood testosterone went from 207.2 to 1,055.5 ng/dL (p<0.0001), and free testosterone from 8.1 to 20.4 pg/mL.
- Semen held steady: before treatment the men averaged 35.2 million sperm per mL with 49.0% motility, and no differences in semen measures were seen during more than a year of follow-up.
- No azoospermia: no man’s sperm count fell to zero while on testosterone plus HCG, whether he used injections or gel.
- Pregnancies: 9 of the 26 men contributed to a pregnancy with their partner during follow-up.
The authors concluded that low-dose HCG appears to maintain semen parameters in men on testosterone therapy, and that using the two together may preserve fertility for men who want it. It is a compact retrospective review with no comparison group. Set beside the 40% azoospermia figure the same authors cite for testosterone alone, its zero is the number that stands out.
Vistara Labs stocks HCG as a lyophilised research material, shipped from within Canada to every province.
What HCG does that testosterone cannot
HCG mimics LH. It stimulates the Leydig cells in the testes to make their own testosterone, which is exactly the signal testosterone therapy switches off. The 2019 review puts it in two lines: HCG stimulates the body’s own testosterone production without compromising sperm production, and low-dose HCG can be used with testosterone therapy to keep testicular testosterone high. The two studies above show what that looks like in numbers: testicular testosterone held in range in 2005, and sperm production held steady in 2013, both with HCG given alongside testosterone.
HCG is measured in international units rather than milligrams, because it is a glycoprotein whose activity does not track its weight exactly. Our HCG explainer covers why, along with its long clinical history in fertility medicine.
Studying HCG alongside testosterone
If your research question is how to keep the testicular axis working while testosterone comes from outside, HCG is the compound both studies used, and our HCG is ready to order. It arrives as a lyophilised powder and is reconstituted with bacteriostatic water; the HCG reconstitution guide walks through the units-per-millilitre arithmetic.
HCG is supplied for laboratory research use only. For more on hormonal research, see Hormonal, Growth Hormone and Body Composition Research and HCG: what it is, why it is measured in IU, and its clinical history.
Frequently asked questions
Why do testicles shrink on TRT?
Testosterone from outside the body turns down the pituitary signals that drive the testes. In a 2005 trial, LH and FSH fell to 5% and 3% of baseline within three weeks and testosterone inside the testes fell 94%. About 80% of testicular volume is sperm-producing tissue, so when that tissue loses its signal the testes get smaller.
Does HCG keep sperm production going on TRT?
In a 2013 Journal of Urology study of 26 men on testosterone therapy plus HCG, no man became azoospermic, semen measures did not change during follow-up, and 9 of the 26 contributed to a pregnancy. The authors concluded that using the two together may preserve fertility.
What HCG doses did the studies use?
In the 2013 study the men received 500 IU of HCG by intramuscular injection every other day alongside their testosterone. The 2005 trial compared 125, 250 and 500 IU every other day, and only the 500 IU group finished above its starting testicular testosterone, at 26% higher. These are the amounts reported in the studies, not recommendations.
How is HCG different from testosterone?
Testosterone therapy supplies the hormone directly and switches off the body’s own LH signal. HCG mimics LH, so it prompts the Leydig cells in the testes to make testosterone themselves, which is how the 2005 trial kept the level inside the testes up.
Where can I buy HCG in Canada?
Vistara Labs supplies HCG as a lyophilised vial, shipped from within Canada to every province. Laboratory research use only.
Sources: Hsieh TC, Pastuszak AW, Hwang K, Lipshultz LI. Concomitant intramuscular human chorionic gonadotropin preserves spermatogenesis in men undergoing testosterone replacement therapy. J Urol. 2013. PMID 23260550. Coviello AD, Matsumoto AM, Bremner WJ, et al. Low-dose human chorionic gonadotropin maintains intratesticular testosterone in normal men with testosterone-induced gonadotropin suppression. J Clin Endocrinol Metab. 2005. PMID 15713727. Patel AS, Leong JY, Ramos L, Ramasamy R. Testosterone is a contraceptive and should not be used in men who desire fertility. World J Mens Health. 2019. PMID 30350483.
References
hCG has an extensive controlled human research literature; it is a glycoprotein hormone rather than a short research peptide.
- Low-dose human chorionic gonadotropin maintains intratesticular testosterone in normal men with testosterone-induced gonadotropin suppressionRandomised trial; 29 normal men on testosterone enanthate randomised to placebo or varying hCG doses.
- A double-blind, placebo-controlled, randomized clinical trial of recombinant human chorionic gonadotropin on muscle strength and physical function and activity in older men with partial age-related androgen deficiencyDouble-blind, placebo-controlled randomised trial in older men with partial age-related androgen deficiency.
Links open the study record on PubMed so the source can be checked directly. Listing a study is not a claim that its findings apply to any other use, product or route of administration. Research use only.
