HCG: an LH substitute with a much longer half-life, and what it is actually for
A placental hormone that binds the same receptor as luteinising hormone and stays in circulation roughly a hundred times longer. That single pharmacokinetic fact is why it is used the way it is, and it explains most of what people find surprising about it.
- Also known as
- Human Chorionic Gonadotropin
- Class
- Ancillary — aromatase inhibitors and SERMs
- Regulatory status
- FDA approved for female infertility and cryptorchidism. Off-label for male TRT support.
- Modelled half-life
- 33 h
- Time to peak
- 6 h
- Formulation
- Aqueous (reconstituted powder)
- Before mixing
- Sealed powder tolerates room temperature in transit, but keep it refrigerated at 2–8 °C (36–46 °F) for anything beyond a few weeks, or frozen for months. Keep it dark — the carton it shipped in is doing a job.
- After mixing
- Once reconstituted with bacteriostatic water: refrigerate at 2–8 °C and use within about 28 days. The benzyl alcohol in bacteriostatic water is what buys that window — plain sterile water has no preservative, so a vial mixed with it should be treated as one sitting only. Kits are usually ten vials: only the one you mixed is on that 28-day clock — the sealed ones keep their own, much longer shelf life, so store them as powder, not as solution.
- What ruins it
- Do not freeze a reconstituted vial. Repeated freeze–thaw is one of the more reliable ways to degrade a peptide.
- Handling caveat
- General handling practice for this formulation. Your supplier’s own insert or COA overrides anything here.
The same receptor, a very different half-life
Established clinical use Human chorionic gonadotropin and luteinising hormone are glycoprotein hormones sharing an identical alpha subunit and differing in the beta subunit that determines receptor specificity. Both bind the LH/hCG receptor on testicular Leydig cells, and the downstream signal is the same: produce testosterone. Functionally, hCG is an LH substitute.
What differs is persistence. Endogenous LH has a circulating half-life measured in tens of minutes and is released in pulses; hCG carries a longer, more heavily sialylated beta-subunit tail that resists renal clearance, and the app models its half-life at about a day and a half. That is why an every-other-day or twice-weekly schedule produces continuous receptor occupancy from a hormone the body normally delivers in bursts — and why very frequent or very high administration can desensitise the receptor, which pulsatile LH does not do.
Intratesticular testosterone is the point
Exogenous testosterone suppresses LH, and without LH the testis stops producing testosterone locally. Serum testosterone can be entirely adequate while the concentration inside the testis — which is normally many times higher than serum and is what spermatogenesis depends on — collapses. Established clinical use That collapse is the mechanism behind both the testicular volume loss and the impaired fertility that accompany testosterone therapy, and it is what hCG addresses: it restores the local signal that the exogenous testosterone removed.
Off-label or community practice Low-amount hCG alongside testosterone therapy for the maintenance of intratesticular testosterone, testicular volume and spermatogenesis is well established in clinical practice and supported by small human studies, and it remains an off-label use — the approved indications are female infertility and cryptorchidism. It is worth being precise about what it does: it maintains function during therapy far more reliably than it restores function afterwards.
Anyone considering testosterone therapy who may want biological children should be having this conversation before starting rather than after. The options are meaningfully different at the two points in time, and that is a fertility specialist's conversation, not a page's.
Two practical consequences people run into
The first is estradiol. Leydig cells express aromatase, so stimulating them produces oestrogen as well as testosterone, and hCG can raise estradiol more than the equivalent rise in serum testosterone would predict. The app records estradiol on the monitoring panel for this compound specifically, and a sensitive assay is what makes that number usable — see the estradiol assay page.
The second is that hCG is the analyte every pregnancy test detects. Anyone using it will test positive on a home or clinic pregnancy test, and hCG can interfere with other immunoassays. This is worth mentioning to a clinician before a test rather than explaining afterwards, and it is a genuine source of alarming false results.
Storage is the third thing that catches people out. It ships as a lyophilised powder and becomes a refrigerated, time-limited solution the moment it is reconstituted; the fact box above carries the app's own rule and its handling caveat. Any of the effects discussed here belongs with the clinician who prescribed it, who is the person who can weigh an estradiol result against everything else on the panel.
The curve, the accumulation ratio and the peak-to-trough figures have a page of their own: HCG half-life and steady state.
The dosing rows the app records
Established clinical use Reproduced from the app’s reference so you can see what it holds, not as a recommendation. Which row applies to a particular person, if any, is a clinical decision this page does not make — and rows describing supraphysiological or post-cycle use are filtered out before this table is built, so what you see here is a subset.
| Label | Amount | Route and frequency | Duration recorded |
|---|---|---|---|
| Fertility on TRT | 250-500IU | 2-3x per week SubQ | Ongoing with TRT |
What the app monitors alongside it
The panel below is the app’s own monitoring note for HCG, verbatim. The analytes in it that have a page here are linked; those pages cover what each one measures, which assay produced it and how to read a trend.
- Monitoring panel
- E2 (HCG aromatizes significantly), Total T. LH/FSH will be suppressed — this is expected.
Drawbacks and risks the app records
From the app's own entry. The estradiol item is the one that most often turns up in practice, and the storage item is the one most often ignored.
- Elevates estrogen (aromatizes significantly in testes)
- Requires refrigeration after reconstitution
- Injection only
- Can cause Leydig cell desensitization at very high doses
- Must stop BEFORE starting SERM PCT
Interaction rules that name HCG
From the app’s interaction data, filtered so no rule naming a compound this site does not publish appears. Not exhaustive, and not a safety clearance: a combination that is not listed is one nobody has documented here, which is not the same as one that is fine. The combination checker has the rest.
HCG Must Stop Before PCT SERMs Begin
HCG should be used during the last 2 weeks of a cycle to prime the testes, then stopped completely before starting Nolvadex or Clomid. Running HCG concurrently with SERMs blunts the PCT response by continuing LH suppression via HCG's action.
What to watch: Timing critical: Stop HCG, wait 2 weeks after last long-ester injection, then start SERMs.
HCG Must Stop Before PCT SERMs Begin
Same as above — HCG and SERMs work at cross purposes during PCT. HCG ends the cycle phase; SERMs begin the PCT phase. They should not overlap.
What to watch: Sequential use only: HCG during cycle, SERMs after.
Gonadorelin and HCG — Choose One for Testicular Maintenance
Both gonadorelin and HCG serve the same purpose on TRT — preserving testicular function. Gonadorelin stimulates LH/FSH from the pituitary; HCG mimics LH directly at the testes. Using both simultaneously is redundant and may cause over-stimulation. Choose one approach.
What to watch: Total T, LH, FSH, E2, testicular volume. Monitor prolactin — over-stimulation can elevate it.
Questions people actually ask
Is HCG a form of testosterone?
No. It is a hormone that instructs the testis to make its own testosterone by binding the receptor luteinising hormone normally binds. That is a different mechanism from taking testosterone, and it is why it maintains testicular function where exogenous testosterone suppresses it.
Does it work in someone whose testes cannot respond?
Not usefully. hCG requires functional Leydig cells to act on. Primary testicular failure — where the testis itself is the problem rather than the pituitary signal — is the case in which stimulating the receptor achieves little, and distinguishing that from secondary hypogonadism is exactly what LH and FSH are measured for. The LH and FSH page covers the distinction.
How long does it stay in the system?
The app models about a day and a half, so roughly a week for a dose to clear. That also governs how long a pregnancy test will read positive after the last administration. The half-life page has the curve.
Why does the app suppress LH and FSH on the panel and call that expected?
Because exogenous testosterone does that regardless, and hCG does not restore the measured pituitary hormones — it replaces the downstream signal. Unmeasurable LH and FSH on testosterone therapy is the expected finding rather than a new one, which is why the app records it as expected rather than flagging it.
Where the load-bearing numbers come from
Named rather than linked. Publisher URLs move, and a citation that resolves to a 404 two years from now is worse than one you can search for by name — every entry below is findable from the title and year alone.
- Shared alpha subunit and LH receptor agonism
- Standard endocrinology references on glycoprotein hormone structure
- Intratesticular testosterone maintenance during testosterone therapy
- Small controlled human studies from the mid-2000s onward, reflected in current hormone-therapy practice
- Approved indications
- The approval string in the fact box is app.html’s own field, reproduced verbatim
- Half-life, formulation and storage rule
- app.html’s TL_PK and TL_STORAGE entries, lifted at build time
HCG and testosterone on different schedules is exactly the situation where a written log beats memory. TherapyLog records both against the same calendar.
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