Tesamorelin vs Ipamorelin: Two Receptors, Two Evidence Bases

Somatotroph cells in the anterior pituitary release growth hormone in response to two stimulatory inputs. Growth-hormone-releasing hormone (GHRH) acts at the GHRH receptor. Ghrelin acts at a separate receptor, the growth hormone secretagogue receptor (GHS-R1a). Somatostatin pushes the other way.

Tesamorelin is a GHRH analogue. Ipamorelin is a synthetic agonist at GHS-R1a. They feed the same output through different receptors, so a study can treat them as two separate variables. A study that swaps one for the other changes the receptor under test.

Raun and colleagues described ipamorelin in 1998 (European Journal of Endocrinology). In conscious swine it released growth hormone with potency and efficacy close to GHRP-6. The difference lay in the other hormones. GHRP-6 and GHRP-2 raised plasma ACTH and cortisol; ipamorelin did not raise them beyond the levels seen after GHRH, even at doses more than 200-fold above its ED50 for growth hormone release. None of the secretagogues tested changed FSH, LH, prolactin or TSH. The authors called it the first GHS-receptor agonist with a selectivity for growth hormone similar to GHRH.

That selectivity is the reason researchers reach for it. A tool that moves one hormone leaves fewer alternative explanations for a downstream result than a tool that moves three.

The human record is thin. Gobburu and colleagues (Pharmaceutical Research, 1999) reported a terminal half-life of about 2 hours in healthy men. Beck and colleagues (International Journal of Colorectal Disease, 2014) ran a phase 2 trial in postoperative ileus after bowel resection: median time to the first tolerated meal was 25.3 hours with ipamorelin and 32.6 hours with placebo, a difference that did not reach significance (p = 0.15). No regulator has approved ipamorelin.

Native GHRH breaks down fast in plasma, in large part through cleavage by dipeptidyl peptidase-4 (DPP-4). Theratechnologies added a hexenoyl group to the N-terminal tyrosine of the full 44-residue sequence; researchers describe the result as stabilised against DPP-4. The original prescribing information reports a half-life of 26 to 38 minutes after repeated administration. Because it acts at the native receptor, the pituitary still releases growth hormone in pulses: Stanley and colleagues (JCEM, 2011) found that two weeks of tesamorelin raised both basal and pulsatile secretion in healthy men, with IGF-1 rising and insulin-stimulated glucose uptake preserved.

Falutz and colleagues (New England Journal of Medicine, 2007) reported that visceral adipose tissue fell 15.2% over 26 weeks with tesamorelin and rose 5.0% with placebo in HIV-infected patients with abdominal fat accumulation. Later reviews note that the reduction reversed after treatment stopped. The FDA approved tesamorelin on 10 November 2010 to reduce excess abdominal fat in HIV-infected adults with lipodystrophy, and approved the F8 formulation, Egrifta WR, on 25 March 2025. In Europe, Ferrer withdrew its marketing application in 2012 after the CHMP gave a provisional view that it could not be approved.

Questions about combining tesamorelin and ipamorelin in people are human-use questions, and Encodex does not answer them. We give no dosing or administration guidance for either compound.

The research question has a published answer at the level of physiology. Bowers and colleagues (Journal of Clinical Endocrinology and Metabolism, 1990) gave 18 healthy men a GHRP hexapeptide (GHRP-6), GHRH or both. Submaximal GHRP plus GHRH released growth hormone synergistically, more than the sum of each alone. In cultured human fetal pituitary cells, Shimon and colleagues (JCEM, 1998) saw only an additive effect, and the authors read that as placing the synergy at the hypothalamic level rather than in the somatotroph itself.

Neither study used tesamorelin or ipamorelin, and we found no published study of the two together. A design that includes both should carry single-agent arms, because a combined arm alone cannot assign an effect to either receptor.

CJC-1295 is another GHRH analogue, built with a drug affinity complex that binds albumin. Teichman and colleagues (JCEM, 2006) reported a half-life of 5.8 to 8.1 days in healthy adults. CJC-1295 and tesamorelin act at the same receptor, so a study that includes both duplicates the GHRH variable instead of adding a new one. Pairing CJC-1295 with ipamorelin follows the same two-receptor logic as tesamorelin with ipamorelin. WADA lists CJC-1295 under S2 as well.

Both peptides arrive lyophilised and reconstitute with standard technique; our reconstitution guide covers it. Blends need extra care with arithmetic. Ipamorelin weighs about one seventh as much per molecule as tesamorelin, so 1 mg of ipamorelin holds about seven times as many molecules as 1 mg of tesamorelin. Equal milligrams in a blend are far from equal molar amounts.

Tesamorelin's length and its N-terminal modification make it harder to synthesise than a pentapeptide, so check the certificate for an observed mass near 5135.9 Da as well as the purity figure. An independent laboratory assays every Encodex lot, by HPLC for purity and by mass spectrometry for identity. The certificate for the lot on your vial is available on request, and the /verify page checks a lot number.