HCG

Human Chorionic Gonadotropin (hCG) is a glycoprotein hormone normally produced by placental syncytiotrophoblast cells during pregnancy. It shares the α-subunit with LH, FSH, and TSH but carries a distinct β-subunit ending in a unique C-terminal peptide that extends serum half-life beyond LH. In AAS protocol design, hCG functions as an exogenous LH analogue — binding the LH receptor (LHCGR) on testicular Leydig cells and stimulating testosterone synthesis directly, bypassing hypothalamic-pituitary signalling.

Three protocol roles, each addressing a different problem:

1. On-cycle preservation — 250–500 IU subcutaneous 2× weekly, throughout the cycle. Mechanism: maintains Leydig-cell enzyme expression and prevents atrophy during HPTA suppression. The published clinical reference is Hsieh et al. 2013, J Urology documenting preserved intratesticular testosterone in TRT users with low-dose adjunct hCG. Preserves testicular volume and shortens post-cycle recovery. Trade-off: dose-dependent intratesticular E2 rise — high hCG doses (1000+ IU) elevate systemic E2 and can override standard AI titration.

2. Pre-PCT bridge — 1500–2500 IU every other day × 10–14 days, after last AAS injection and before SERM phase. Mechanism: reactivates Leydig-cell enzymes that have been dormant during cycle; produces responsive tissue substrate for the SERM to work against. The preferred approach when on-cycle hCG was not used and cycle duration exceeded 16 weeks. SERM-only PCT after long cycles without hCG bridge fails predictably — LH rises but Leydig cells cannot respond because the steroidogenic machinery has decayed.

3. Post-cycle salvage — 1500 IU every other day × 2 weeks, then reassess. For users presenting at week 8 post-PCT with elevated LH and persistently low total testosterone — the primary hypogonadism picture indicating Leydig-cell failure. Formal endocrinology referral warranted if no response.

Clinical pharmacology details:

Serum half-life of hCG is approximately 24 hours after intramuscular injection, 33 hours after subcutaneous (longer than expected because of the C-terminal peptide extension). The longer SubQ half-life supports the standard 2× weekly dosing for on-cycle use. hCG acts primarily at testicular Leydig cells; some evidence suggests minor activity at FSH receptors at high doses, supporting partial spermatogenesis preservation but not replacing FSH-specific therapy where fertility is the primary endpoint.

Product quality considerations:

hCG preparations show substantial inter-lot bioactivity variance even from reputable sources. Reconstituted hCG has practical shelf life of approximately 30 days refrigerated, after which bioactivity drops below threshold for Leydig stimulation. If bloodwork at week 4 on hCG protocol shows no rise in intratesticular signal (proxy markers: estradiol rise, testicular volume stability), the problem is often product quality rather than dose or protocol.

Bloodwork schedule on hCG protocols:

Total testosterone, free testosterone, sensitive estradiol (LC-MS/MS), LH, FSH at week 4 of any hCG protocol. Elevated E2 with on-target total T indicates hCG dose reduction is warranted before AI dose increase. Flat E2 despite hCG administration suggests product-quality failure rather than individual non-response.

Mechanism distinction vs SERM:

hCG bypasses hypothalamic-pituitary signalling and stimulates Leydig cells directly. SERMs (tamoxifen, clomiphene) lift the hypothalamic feedback brake and restart endogenous LH/FSH signalling. The interventions address different points in the HPTA cascade — hCG restores testicular testosterone synthesis without restarting the central signal; SERMs restart the central signal but require responsive Leydig cells to work. Combined or sequential use is common in extended-cycle recovery protocols.