GH / IGF-1 AXIS / COMPARE
Three Peptides, Side by Side
Where tesamorelin, ipamorelin and MOTS-c converge, where they diverge, and how far the evidence behind each one actually reaches.
The short version
This page lines up tesamorelin, ipamorelin, and MOTS-c on the dimensions that matter most when reading research peptides: what kind of molecule each one is, where it sits on the GH-axis pathway, how strong the human evidence is, how it was administered in studies, its regulatory status, and its single most important caution. The headline finding is simple. All three are studied in the context of the GH/IGF-1 axis and body composition, but they are at very different stages of evidence and address the axis from distinct points of entry: tesamorelin is a pituitary stimulator with a real but narrow FDA approval and replicable RCT data; ipamorelin is a selective pituitary secretagogue with human PK data and one failed Phase 2 trial; MOTS-c is a mitochondrial-encoded peptide with no human interventional trials at all. None is an approved general medicine, and none is presented here with a human dose.
The comparison matrix
| Dimension | Tesamorelin | Ipamorelin | MOTS-c |
|---|---|---|---|
| Peptide class | Synthetic GHRH analogue (44 aa) | Synthetic GHS-R1a agonist / growth hormone secretagogue (5 aa) | Mitochondrial-derived peptide (16 aa) |
| Axis entry point | Hypothalamus → pituitary GHRH-R → endogenous GH pulses | Pituitary GHS-R1a → endogenous GH pulses | Mitochondria → AMPK → AICAR → skeletal muscle / nucleus |
| Most-studied in | Visceral fat and liver fat in HIV-associated lipodystrophy | GH selectivity, bone growth (rats), postoperative ileus (human), chemotherapy weight loss (ferrets) | Skeletal muscle metabolism, aging, physical performance (mice); CV biomarker association (humans) |
| Evidence base | 5 RCTs in HIV adults; meta-analysis [1]; short healthy-volunteer mechanistic study [4] | Human PK (n=8, acute IV) [9]; failed Phase 2 RCT (n=114, bowel surgery) [8]; preclinical [10][11][12] | Mice [13][16][17]; human observational cohort (n=94, hemodialysis) [14]; reviews [15] |
| Regulatory status | FDA-approved (HIV lipodystrophy only); all other uses off-label [2] | Not approved anywhere; removed from 503A compounding list 2024 [11] | Not approved anywhere [15] |
| WADA status | S2 prohibited, in- and out-of-competition [2] | S2 prohibited, in- and out-of-competition [11] | Prohibited (hormone/metabolic-modulator category) [15] |
| Key caution | Approval is indication-specific; effect reverses on discontinuation; long-term IGF-1 oncologic data limited [1][5] | Only Phase 2 failed; no human subcutaneous PK; class-level cardiac signal from related GHS-R1a agonist [7][8] | No human interventional trials; no human PK; all body-composition claims are extrapolated from rodents [14][15] |
Peptide class and axis entry point
The three peptides intervene at entirely different levels of the GH/IGF-1 cascade. Tesamorelin mimics the hypothalamic signal itself — GHRH — at the pituitary GHRH receptor, stimulating endogenous GH in a pulsatile, physiological pattern [1][4]. Ipamorelin acts at a separate pituitary receptor (GHS-R1a, the ghrelin receptor) to trigger the same downstream GH pulse but through a complementary, additive pathway [11]. The two are pharmacologically distinct: a GHRH analogue and a growth hormone secretagogue can be (and often are) combined in research because they hit different switches on the same somatotroph cell.
MOTS-c does not engage the pituitary axis at all. It is a mitochondrial-encoded peptide whose primary metabolic action runs through AMPK activation in skeletal muscle, upstream of anything the pituitary does [15][17]. It belongs on this desk because it addresses overlapping downstream questions about body composition, muscle mass, and insulin sensitivity — but through a fundamentally different signaling origin.
Evidence base
This is where the three genuinely separate. Tesamorelin has the most controlled human evidence: five RCTs in an HIV population, a 2026 meta-analysis pooling those results [1], and a mechanistic study in healthy men [4]. The limitations are that all efficacy data are in a specific clinical population and all effects reverse on discontinuation [5].
Ipamorelin has two human datasets: an acute IV PK/PD study in 8 healthy males per dose level [9] and a 114-patient Phase 2 RCT that missed its primary endpoint [8]. The dominant research-use pattern — subcutaneous self-administration — has no published human characterization at all.
MOTS-c has the earliest human data: a 94-patient observational biomarker association in hemodialysis patients [14] and several strong mouse studies [13][16][17]. No human interventional trial has been conducted [15].
Regulatory and sport status
The regulatory picture varies sharply across the three. Tesamorelin holds an FDA approval — for HIV-associated lipodystrophy only — making it a legitimate prescription medicine in that narrow indication and an off-label research compound in every other context [2]. Ipamorelin was never approved and in 2024 lost its eligibility for compounding pharmacy production under Section 503A, tightening the already-limited legal pathway for clinical use [11]. MOTS-c has no approved indication anywhere and is sold only as a research chemical [15].
All three are prohibited in sport. Tesamorelin and ipamorelin are explicitly listed under WADA category S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), prohibited in- and out-of-competition [2][11]. MOTS-c is covered under the broader hormone and metabolic-modulator prohibition applied to non-approved peptides [15].
Key cautions, side by side
Each compound carries a defining limitation that matters most when reading its evidence.
For tesamorelin, the caution is scope: the approval and the replicated trial data exist, but they apply to a specific patient population (HIV-positive adults on antiretroviral therapy with lipodystrophy). Effects in the general population are unestablished by controlled trials, effects reverse on discontinuation, and long-term IGF-1 elevation carries a theoretical oncologic concern with limited long-run data [1][2][5].
For ipamorelin, the caution is the gap between mechanism and clinical reality: it is pharmacologically elegant and GH-selective in preclinical models, but its one Phase 2 trial failed [8], no approved indication exists, subcutaneous human pharmacokinetics are uncharacterized, and a class-level cardiac signal from a related GHS-R1a agonist in rats has not been resolved for ipamorelin itself [7].
For MOTS-c, the caution is evidence stage: the mechanisms are interesting, the mouse data are genuinely striking, and the 2024 molecular-target identification [13] is a real advance — but there is no interventional human trial, no human PK, and the claim that exogenous MOTS-c in humans will produce what it produces in aged mice requires the kind of clinical translation that has not happened yet [14][15].
Reading them together, the lesson is consistent: the GH-axis peptide field offers coherent mechanisms and often impressive preclinical signals, with clinical translation that lags substantially behind — and varies widely even within this small group of three.