Comparison · 1-44 vs 1-29
Tesamorelin vs Sermorelin: Full-Length GHRH(1-44) Analogue vs Truncated GHRH(1-29)
Both are GHRH-based peptides aimed at the same receptor, but they differ in length, stabilization, and the depth of their evidence. The structural and research contrast, cited.
The short version
Both tesamorelin and sermorelin are peptides that copy GHRH (the brain's "make growth hormone" signal) and act on the same receptor in the pituitary. The tesamorelin vs sermorelin difference is mostly about length and durability. Tesamorelin reproduces the full 44-amino-acid hormone and adds a chemical cap on one end that stops the body from breaking it down quickly; sermorelin is a shorter 29-amino-acid fragment without that protection [8]. Tesamorelin also carries a far deeper evidence base — large FDA trials in HIV patients — whereas this site only summarizes the published tesamorelin record.
Structure: 44 amino acids versus 29
The headline structural difference is sequence length. Tesamorelin is a synthetic analogue of the full-length GHRH(1-44) — all 44 amino acids of the native hormone — while sermorelin corresponds to the truncated GHRH(1-29), the first 29 residues [8]. GHRH(1-29) retains the receptor-binding core, which is why both peptides can stimulate the GHRH receptor, but the molecules are not the same length.
The more consequential difference is what sits on tesamorelin's N-terminus. A clinical review describes tesamorelin as a stabilized full-length GHRH(1-44) analogue, distinct from sermorelin's truncated GHRH(1-29), whose N-terminal trans-3-hexenoic acid modification confers resistance to DPP-IV [8]. Sermorelin carries no such modification. Tesamorelin's full molecule is a 5,135.9-Da peptide with the free-base formula C221H366N72O67S and the CAS number 218949-48-5 — figures specific to the 44-residue, N-terminally modified analogue, not to the shorter sermorelin fragment.
Stabilization: the DPP-IV-resistant N-terminus
Native GHRH is cleaved by dipeptidyl peptidase-IV (DPP-IV, an enzyme that snips peptides at their second amino-acid position) almost as fast as it is released, which sharply limits how long an unmodified GHRH peptide stays active. Tesamorelin's trans-3-hexenoyl N-terminal group blocks that cleavage, extending its plasma activity relative to native GHRH [8]. Sermorelin, as the unmodified GHRH(1-29) fragment, is subject to the same rapid DPP-IV inactivation that limits native GHRH.
This is the design logic that separates the two peptides: tesamorelin was engineered specifically to survive DPP-IV long enough to drive a sustained downstream IGF-1 signal [16], while sermorelin's pharmacology reflects the shorter, unprotected fragment. The practical consequence shows up in tesamorelin's pharmacokinetics — the peptide still clears plasma within minutes, yet the IGF-1 elevation it triggers persists across a once-daily interval, which is the schedule used in every tesamorelin trial [16].
Evidence base: where the two diverge most
On structure the peptides are cousins; on evidence they are not comparable within this record. Tesamorelin carries an unusually deep clinical dossier for its class — two pivotal Phase 3 RCTs, a JAMA hepatic-fat trial, a healthy-men mechanistic study, and a 2026 meta-analysis of five RCTs — supporting FDA approval in 2010 for HIV-associated lipodystrophy [1][3][4][5][13]. In the pivotal trial, 2 mg/day cut visceral fat 15.2% and raised IGF-1 81% [1]. The 2026 meta-analysis pooled a visceral-fat reduction of -27.71 cm2 and a hepatic-fat-fraction change of -4.28% across five trials [13], and a pooled predictor analysis found the odds of reducing visceral fat below 140 cm2 were 3.9-fold greater with tesamorelin than placebo [11]. That depth of human evidence is specific to tesamorelin.
This site documents only the tesamorelin literature, so it makes no efficacy claim about sermorelin. The defensible comparison is structural and pharmacological: tesamorelin is the longer, DPP-IV-stabilized full-length analogue; sermorelin is the shorter, unmodified GHRH(1-29) fragment [8]. Where the two are alike is the receptor they target and the general direction of effect — endogenous GH release — not the magnitude or quality of evidence, which for tesamorelin spans more than a dozen peer-reviewed studies. For the underlying biology shared by both, see how tesamorelin works.
What both share, and the regulatory line
Both peptides aim at the same target — the GHRH receptor on pituitary somatotrophs — and both work by stimulating endogenous growth-hormone release rather than supplying GH directly [4][6]. That shared mechanism is why they are routinely discussed together.
The regulatory status is not shared. Tesamorelin is FDA-approved, but only to reduce excess abdominal fat in HIV-associated lipodystrophy; all other uses are off-label [5][14]. Tesamorelin is also prohibited in sport under the WADA Prohibited List (category S2) as a GHRH analogue, in- and out-of-competition. Research-grade tesamorelin supplied for laboratory use is not the approved finished drug product and is not approved for human self-administration.