--------|-------------|-----| | Sperm morphology | +17% improvement | No change | | Sperm concentration | Stable | -61% decrease | | Natural hormone production | Preserved | Suppressed | | Fertility potential | Maintained/improved | Severely compromised |
Read that again: TRT decreased sperm concentration by 61%. That's not a small decline — that's approaching sterility for many men.
Why TRT Destroys Fertility
The mechanism is straightforward.
Your brain monitors testosterone levels through the HPT (hypothalamic-pituitary-testicular) axis. When it senses adequate testosterone, it reduces the signals (LH and FSH) that tell your testes to produce more.
When you inject external testosterone: 1. Blood testosterone rises 2. Brain senses "enough testosterone" 3. LH and FSH drop to near zero 4. Testes receive no signal to function 5. Sperm production stops 6. Testes physically shrink from disuse
90% of men on TRT become azoospermic — meaning zero sperm in their ejaculate. This can happen within months of starting treatment.
The fertility shutdown is a feature of how TRT works, not a side effect. You can't have high-dose external testosterone without suppressing natural production.
Why GLP-1s Preserve (And May Improve) Fertility
GLP-1 medications work through completely different mechanisms. They: - Don't interact with the HPT axis - Don't suppress LH or FSH - Don't signal the brain to reduce testicular function - Target appetite and metabolism, not reproductive hormones
Your testes continue functioning normally. Sperm production continues uninterrupted.
But the Ljubljana data suggests GLP-1s may actually improve fertility, not just preserve it. The 17% improvement in normal sperm morphology suggests metabolic improvement benefits reproductive function.
Possible mechanisms: - Reduced oxidative stress from weight loss - Improved metabolic environment for sperm production - Reduced inflammation - Better blood flow to reproductive organs - GLP-1 receptors in testes may have direct effects
What This Means Practically
If You Definitely Want Kids Soon
Do not start TRT. Even "TRT with HCG" (a common protocol to maintain fertility) is risky — HCG helps but doesn't guarantee preserved fertility.
GLP-1s give you weight loss, potential testosterone improvement, and fully preserved fertility. You can conceive on a GLP-1 without any concerns about sperm production.
If You Might Want Kids Someday
The same logic applies. If there's any possibility you'll want biological children in the future — even if it seems unlikely now — TRT creates a real risk.
Some men recover fertility after stopping TRT. Many don't, or take 1-2+ years to recover. Some never recover.
Why gamble when there's an alternative that doesn't require the gamble?
If You're Done Having Kids
If you've had a vasectomy, or are absolutely certain you don't want (more) children, this consideration doesn't apply to you.
For these men, TRT's fertility suppression is irrelevant. The comparison shifts to other factors: cardiovascular effects, weight loss, mechanism of testosterone increase.
Recovery After TRT: The Harsh Reality
Men considering TRT often believe they can simply stop if they want to have kids later. This is partially true but oversimplified.
Recovery timeline after stopping TRT: - 3-6 months: LH and FSH start recovering - 6-12 months: Sperm production may restart - 12-24 months: Sperm counts may approach pre-TRT levels - Never: Some men don't fully recover
Factors affecting recovery: - Duration of TRT use (longer = harder recovery) - Age (older = harder recovery) - Whether HCG was used alongside TRT - Individual variation (unpredictable) - Pre-TRT fertility status
Studies suggest 65-90% of men eventually recover sperm production after TRT. That means 10-35% may have permanent impairment.
Would you take a medication with a 10-35% chance of permanent sterility if an alternative existed? For most men wanting kids, that's not an acceptable risk.
The Conversation Clinics Aren't Having
Many men's health clinics are eager to prescribe TRT. The fertility conversation is often a footnote:
"TRT may affect fertility. We can add HCG if that's a concern."
This undersells the severity. It should be:
"TRT will almost certainly make you temporarily infertile and may permanently impair your fertility. HCG reduces this risk but doesn't eliminate it. If you want biological children in the future, there are alternatives that don't carry this risk."
GLP-1 medications should be part of that conversation for men with obesity-related low testosterone. They address the testosterone problem (through weight loss) without the fertility sacrifice.
Decision Framework
Choose GLP-1 first if: - You want children now - You might want children in the future - You're not 100% certain you're done having kids - Your low testosterone is obesity-related - You can wait months for testosterone improvement
Consider TRT only if: - You've completed your family (vasectomy or otherwise) - GLP-1s haven't normalized testosterone despite significant weight loss - You have primary hypogonadism (non-obesity cause) - Fertility is genuinely not a consideration
Don't Let Clinics Rush You
If a clinic is pushing TRT without discussing: - Fertility implications in detail - GLP-1s as an alternative for obesity-related low T - Recovery uncertainty after stopping
...consider getting a second opinion. Your future family planning shouldn't be an afterthought.
The data is clear: GLP-1s preserve and may improve fertility. TRT severely compromises it. For men who want biological children, this should be a primary factor in treatment decisions.
The Bottom Line
GLP-1 medications: +17% sperm morphology improvement, fertility fully preserved, can conceive during treatment.
TRT: -61% sperm concentration, 90% become azoospermic, uncertain recovery after stopping.
If kids are in your future — or might be — this isn't even a close call.
Related Articles: - GLP-1 vs TRT: The Head-to-Head Comparison for Men - 77% of Men Normalized Testosterone on GLP-1s — Without TRT - GLP-1s and Sexual Function: What the Research Shows
Last updated: January 2026
Sources: Gregorič et al., Ljubljana fertility comparison study
Medical disclaimer: This content is for informational purposes only. Discuss fertility considerations with a reproductive endocrinologist.