Ipamorelin vs Tesamorelin: Growth Hormone Secretagogue Comparison

Ipamorelin and tesamorelin both raise growth hormone, but they do it through different receptors on pituitary somatotrophs.

Ipamorelin is a pentapeptide GHRP-receptor agonist (Aib-His-D-2-Nal-D-Phe-Lys-NH2). Raun et al. showed that it releases GH from rat pituitary cells with potency similar to GHRP-6, that GHRP and GHRH antagonists place it on a GHRP-like receptor, and that in swine it matched GHRP-6 for GH release while, unlike GHRP-6 and GHRP-2, it did not raise ACTH or cortisol even at doses more than 200-fold the GH ED50 (PMID: 9849822). Those ACTH and cortisol data are from animals (anaesthetized rats and conscious swine), not from a human body-composition study. The ghrelin-receptor (GHSR-1a) pathway is the molecular contrast with GHRH analogs.

Tesamorelin is a GHRH analog: GHRH(1-44) with a trans-3-hexenoic acid N-terminal modification that slows DPP-IV degradation relative to native GHRH. It binds pituitary GHRH receptors, increases endogenous GH and IGF-I, and in HIV lipodystrophy trials that GH/IGF-I rise is accompanied by selective visceral fat loss (PMID: 18057338, PMID: 20554713). It does not act at GHSR-1a.

The receptors differ, so combining them is still a hypothesis. No published trial has tested ipamorelin plus tesamorelin.

Tesamorelin: Phase 3 visceral-fat program

The NEJM Phase 3 trial randomized 412 HIV-infected patients with abdominal fat accumulation to tesamorelin 2 mg or placebo subcutaneously daily for 26 weeks. Visceral adipose tissue fell 15.2% with tesamorelin and rose 5.0% with placebo; triglycerides fell 50 mg/dL versus a 9 mg/dL rise; the total-to-HDL cholesterol ratio improved; IGF-I rose 81.0% versus a 5.0% fall (P<0.001 for these comparisons). Glycemic measures did not differ significantly. More tesamorelin-treated patients withdrew because of an adverse event. Trial registration: NCT00123253 (PMID: 18057338).

The JCEM pooled analysis combined two multicenter Phase 3 studies (n=806 randomized 2:1 to tesamorelin 2 mg or placebo). At week 26, VAT change was −24 ± 41 versus +2 ± 35 cm² (treatment effect −15.4%, P<0.001). Abdominal subcutaneous adipose tissue did not change meaningfully (treatment effect −0.6%). Triglycerides fell with a −12.3% treatment effect; IGF-I rose 108 ± 112 versus −7 ± 64 ng/mL. In patients who continued tesamorelin to week 52, VAT reduction was maintained (−17.5 ± 23.3% from original baseline). Glucose parameters showed no clinically meaningful between-group differences at weeks 26 and 52 (PMID: 20554713).

Stanley et al. randomized 50 antiretroviral-treated HIV patients with abdominal fat accumulation to tesamorelin 2 mg or placebo for 6 months. Tesamorelin reduced VAT (treatment effect −42 cm², P=0.005) and liver fat (median lipid-to-water percentage −2.0% versus +0.9% placebo, P=0.003). Fasting glucose rose at 2 weeks but was not significantly different at 6 months (PMID: 25038357, NCT01263717).

Falutz et al. 2008 reported a 52-week safety-and-effects extension after the first 26-week trial: continued tesamorelin maintained VAT reduction; switching to placebo was associated with return toward baseline adiposity (PMID: 18690162).

Ipamorelin: human PK/PD and a negative ileus RCT

Gobburu et al. infused ipamorelin over 15 minutes at five dose rates (4.21 to 140.45 nmol/kg) in eight healthy men per dose. Pharmacokinetics were dose-proportional, with a terminal half-life of 2 hours. GH showed a single episode peaking at 0.67 hours. An indirect-response model gave SC50 214 nmol/L for half-maximal GH stimulation (PMID: 10496658). The paper reports GH stimulation in volunteers, not body composition, muscle, or fat outcomes.

Beck et al. ran a multicenter, double-blind Phase 2 ileus trial (NCT00672074): intravenous ipamorelin 0.03 mg/kg versus placebo twice daily from postoperative day 1 to 7 or discharge after bowel resection. 117 patients were enrolled; 114 formed the safety and modified intent-to-treat sets. Median time to first tolerated solid meal was 25.3 versus 32.6 hours (P=0.15). Treatment-emergent adverse events occurred in 87.5% (ipamorelin) versus 94.8% (placebo). The trial was well tolerated and negative on the key efficacy analysis (PMID: 25331030). ClinicalTrials.gov lists the study completed (2009) for postoperative ileus; ipamorelin was not approved for this or any other indication.

PubMed has no randomized ipamorelin trial for muscle growth, visceral fat, or adult GH deficiency. Those uses rest on GH-axis pharmacology, not on published efficacy trials.

Tesamorelin. In the 806-patient pooled Phase 3 analysis, treatment was described as generally well tolerated, without clinically meaningful glucose differences at weeks 26 and 52, despite the IGF-I rise (PMID: 20554713). The NEJM trial found overall adverse-event rates similar between groups but more withdrawals for adverse events on tesamorelin (PMID: 18057338). The Stanley liver-fat RCT found a transient fasting-glucose increase at 2 weeks that was not significant at 6 months (PMID: 25038357). The 52-week extension reported no significant long-term safety concerns in that HIV-lipodystrophy population (PMID: 18690162). Those safety findings apply to HIV-associated lipodystrophy and to the 2 mg daily subcutaneous regimen used in the trials.

Ipamorelin. Gobburu et al. did not report serious safety problems at the infused volunteer doses (PMID: 10496658). In the ileus RCT, treatment-emergent adverse events were slightly less common than with placebo, and the study missed its efficacy endpoint (PMID: 25331030). Published ipamorelin trials do not establish long-term human safety, cancer follow-up, or metabolic safety with chronic GH-axis stimulation. Swine ACTH and cortisol selectivity (PMID: 9849822) is not chronic human safety data.

Neither peptide has a published combination-safety dataset with the other.

Tesamorelin is FDA-approved as Egrifta / Egrifta SV to reduce excess abdominal fat in HIV-infected patients with lipodystrophy, based on the Phase 3 visceral-fat program above. The labeled indication is HIV-associated lipodystrophy, not general obesity or anti-aging use.

Ipamorelin has never received FDA approval. The only completed, published efficacy RCT is the negative postoperative-ileus study (PMID: 25331030, NCT00672074).

Both act on the GH axis. WADA status for GH-related substances should be checked on the current Prohibited List.

Tesamorelin has human, indication-specific evidence for reducing CT-measured visceral fat in HIV-associated lipodystrophy, plus liver-fat data from a 50-patient RCT. Phase 3 endpoints were VAT and related metabolic measures, not muscle hypertrophy, so those trials do not answer which peptide is better for muscle growth.

Ipamorelin is better documented as a selective GHSR-1a agonist in preclinical GH-release assays and as a human GH secretagogue in a PK/PD model. It is not better documented for fat loss or muscle. The ileus program missed its primary endpoint and did not lead to approval.

No RCT compares the two. No published ipamorelin trial tests muscle or visceral fat. Tesamorelin’s VAT effect outside HIV lipodystrophy is a separate question from the approval trials.