Issue 03 · The Axes
It's Not Just That It Falls. It's Why — and That Changes What to Do About It.
"Three types of low T — only one of them needs testosterone"
Testosterone production is a three-tier system: hypothalamus → pituitary → testes. It's called the HPG axis (hypothalamic-pituitary-gonadal).
At the top, kisspeptin neurons in the hypothalamus drive GnRH (Gonadotropin-Releasing Hormone) release. GnRH travels to the pituitary and triggers the release of LH (Luteinizing Hormone) and FSH (Follicle-Stimulating Hormone). LH signals the Leydig cells in the testes to produce testosterone. FSH drives sperm production.
Testosterone then feeds back to the hypothalamus and pituitary, telling them to reduce GnRH and LH production — a self-regulating loop.
This is important: testosterone doesn't just "happen." It's the output of a signaling cascade, and that cascade has multiple failure points.
Primary hypogonadism: The problem is in the testes. The testes can't produce adequate testosterone even when signaled normally. LH and FSH are high — the pituitary is working, it's shouting at the testes — but the testes aren't responding. This is where TRT is genuinely necessary. The upstream axis works; the downstream producer doesn't.
Secondary hypogonadism: The problem is at the hypothalamus or pituitary. LH is low or low-normal, testosterone is low, and the testes are capable of producing if they receive the signal. This is the category where interventions upstream of TRT make sense: gonadorelin (synthetic GnRH), kisspeptin, or clomiphene — all of which can restore LH pulsatility and testosterone production without suppressing the axis.
Functional hypogonadism: This is the one most men don't know about, and it's probably the most common category among men who are otherwise healthy. The axis is suppressed by lifestyle factors — not by pathology. The result looks like secondary hypogonadism on labs, but the fix is not hormonal intervention. It's removing the suppressor.
The most common suppressors:
If you have low testosterone and any of the above apply to you — especially sleep apnea or significant visceral fat — treating those factors first can restore meaningful testosterone without any hormonal intervention.
TRT works. It delivers testosterone reliably, and it resolves symptoms in men with genuinely low testosterone. I'm not arguing against it for men who need it.
But the mechanism matters for the decision.
When you inject testosterone, your hypothalamus detects high circulating testosterone and reduces GnRH output. Your pituitary detects high testosterone and reduces LH and FSH. Your testes receive no LH signal, so Leydig cells stop producing testosterone. Sertoli cells receive no FSH, so sperm production drops or stops.
The result: testicular atrophy (the testes have no signal to respond to and no function to maintain), loss of endogenous testosterone production, and — for men who care about it — infertility.
Most TRT clinics don't emphasize this clearly enough. TRT is not supplementing your testosterone; it is replacing your axis.
For men who have made that decision knowingly and are fine with the tradeoffs, this is fine. For men who don't know what they're deciding — it's a problem.
Two peptides are relevant here, depending on your situation.
Gonadorelin (synthetic GnRH) is used alongside TRT to maintain the downstream signal. When you're on TRT, your pituitary stops releasing LH naturally. Gonadorelin replaces that pulsatile GnRH signal, which tells the pituitary to release LH, which signals the testes to maintain their function. Historically, this role was filled by hCG (which mimics LH directly) — but FDA access restrictions on compounded hCG have pushed most practitioners toward gonadorelin.
The key word is pulsatile. Gonadorelin, like GnRH itself, must be given as pulses, not continuously. Continuous GnRH agonism paradoxically suppresses the axis — this is actually how prostate cancer is treated (Lupron/leuprolide given continuously to suppress testosterone). At 2–3 injections per week, it maintains testicular function; daily would have the opposite effect.
Kisspeptin targets further upstream — it restores the hypothalamic signal that drives GnRH production. For men with functional or mild secondary hypogonadism who want to try restoring the axis before committing to TRT, kisspeptin is one of the more promising emerging options. The clinical data is building; it's not yet widely available as a compounded peptide, but that's changing.
One more piece most men learn too late: testosterone and estrogen are not enemies.
Some estradiol (E2) is essential for men — it supports libido, cognitive function, bone density, and cardiovascular health. The problem is not estrogen; it's the ratio and the context.
The more visceral fat you carry, the more aromatase enzyme you have, the more your testosterone converts to estrogen. This creates a feedback loop: more fat → more estrogen → more suppression of GnRH/LH → lower testosterone → easier fat accumulation.
Many men on TRT are given aromatase inhibitors to "control estrogen." Some of them need it. A lot of them are being over-medicated — too much AI causes joint pain, poor lipid profiles, erectile dysfunction, and mood problems that look exactly like the things TRT is supposed to fix. If you're on TRT and an AI and you're still not feeling right, the AI is worth evaluating.
The simpler answer, before any medication: body fat reduction lowers aromatase activity and often improves the testosterone-to-estrogen ratio without pharmaceutical intervention.
If you're going to evaluate your testosterone status, this is the minimum panel:
LH and FSH are what most primary care doctors skip. They're the difference between knowing where the axis broke and just knowing the output number.
We'll step away from hormones and into repair. Why injuries heal slower as you age — the specific biological bottleneck most men don't know about — and the two peptides that target it directly. If you've had an injury that won't resolve, next issue is the mechanism behind it.