Between late 2024 and mid-2026, five independent systematic reviews examined the same question: what do GLP-1 receptor agonists do to male reproductive hormones?
The question matters because functional hypogonadism affects an estimated 30–50% of men with obesity. The default treatment has been testosterone replacement therapy — which suppresses gonadotropins, shuts down spermatogenesis, and treats the number while ignoring the metabolic machinery that produced it.
The reviews converged. GLP-1 receptor agonists increase testosterone in men with metabolic dysfunction without suppressing the hypothalamic-pituitary-gonadal axis. Some improve semen parameters. All preserve fertility. Natesh’s ENDO 2026 presentation across five randomized controlled trials found no evidence of HPG axis suppression in any study.
Two Head-to-Head Trials
Gregorič et al. randomized 25 obese men with type 2 diabetes and functional hypogonadism to weekly semaglutide (1 mg) or intramuscular testosterone undecanoate for 24 weeks. Both groups increased total testosterone. But semaglutide improved sperm morphology — from 2% to 4% normal forms — while testosterone therapy worsened semen parameters across the board. At baseline, both groups had sperm quality below the WHO fifth percentile.
Cannarella et al. ran a 16-week controlled pilot of tirzepatide in men with obesity-associated metabolic hypogonadism. Total testosterone rose from 9.8 to 13.9 nmol/L. Hypogonadism reversed in every treated patient. The increases in free and total testosterone exceeded those in the testosterone replacement comparator group.
“The presence of hypogonadism, or low testosterone, was reversed in all patients that were treated with tirzepatide, which was really a remarkable finding.”
— Rossella Cannarella, University of Catania
The Drugs Diverge
The three GLP-1 receptor agonists with reproductive data don’t work identically. Liraglutide actively elevates LH and FSH — it doesn’t just permit gonadotropin recovery, it drives it. Semaglutide maintains stable gonadotropin levels without elevation or suppression. Tirzepatide, a dual GIP/GLP-1 receptor agonist, recruits additional metabolic pathways and produces the largest testosterone gains.
All three preserve spermatogenesis. Testosterone replacement suppresses it.
A finding from Jensterle’s analysis: semaglutide’s improvements in sperm morphology were not correlated with changes in body weight or circulating testosterone concentrations. The mechanism exceeds metabolic restoration. Direct GLP-1 receptor expression has been identified on Leydig cells, Sertoli cells, and in kisspeptin-GnRH signaling pathways — both central and peripheral action. The axis isn’t simply recovering because the metabolic burden lifted. Something is being actively restored.
The Asymmetry
These data exist because someone chose to measure them. Testosterone, LH, FSH, and semen parameters were included as endpoints — not always primary, often secondary or exploratory, but present. The question was asked. Five systematic reviews could be written because the underlying trials collected the data.
Another drug class targets the same metabolically compromised, inflammation-driven population.
NLRP3 inflammasome inhibitors reduce the hypothalamic inflammation that disrupts kisspeptin signaling and suppresses GnRH pulsatility. The preclinical evidence connecting NLRP3 to testicular dysfunction is extensive: Sertoli cell NLRP3 activation drives IL-1β release, which suppresses Leydig cell steroidogenesis. Four independent papers have demonstrated bidirectional feedback between kisspeptin and NLRP3 across seven tissue types. Academic reviews describe the mechanism. They propose targeting it.
The clinical pipeline has 286 registered molecules. At least 30 are in active development. Thirteen are brain-penetrant — reaching the hypothalamic territory where kisspeptin neurons reside and gliosis disrupts GnRH pulsatility. Human data from parunoflast (Phase 2a) and ruvonoflast (RESOLVE-1, 176 patients, 24 weeks) show 80% hsCRP reduction without weight loss, confirming inflammation-adiposity dissociation as a class effect.
Reproductive endpoints across all 286 molecules, all registered trials, all clinical programs: zero.
| GLP-1 Receptor Agonists | NLRP3 Inhibitors | |
|---|---|---|
| Target population | Obesity, T2D, metabolic syndrome | Obesity, T2D, metabolic syndrome, CV disease |
| Hypothalamic inflammation | Reduces indirectly via metabolic restoration | Reduces directly via inflammasome blockade |
| Preclinical reproductive mechanism | GLP-1R on Leydig/Sertoli cells; KP-GnRH pathway | NLRP3→IL-1β→Leydig suppression; KP-NLRP3 loop |
| Weight reduction | Yes (5–22%) | No (class effect) |
| Testosterone measured in trials | Yes — multiple RCTs | 0 |
| LH / FSH measured | Yes | 0 |
| Semen parameters measured | Yes | 0 |
| Systematic reviews on reproductive endpoints | 5 (2024–2026) | 0 |
| Clinical-stage molecules | 5+ approved or late-stage | 286 registered, 0 approved |
Same patient population. Overlapping pathology. Shared mechanistic territory in the hypothalamus and the testis. One field measured reproductive endpoints. The other didn’t. The invisible endpoint becomes visible only through comparison with a field that chose to look.
The Widest Distribution, the Least Data
There is one more asymmetry, and it sits inside the GLP-1 field itself.
The reproductive data — the five systematic reviews, the head-to-head trials, the gonadotropin measurements — all come from injectable molecules. Semaglutide requires weekly subcutaneous injection. Liraglutide requires daily injection. Tirzepatide requires weekly injection. They are effective drugs, but injection limits reach.
Orforglipron is an oral nonpeptide GLP-1 receptor agonist. No injection. No refrigeration. It is the molecule designed for the widest possible adoption — the one that will reach men who would never accept a weekly injection.
ATTAIN-1 · ATTAIN-MAINTAIN · ATTAIN-Hypertension