Tesamorelin and CJC-1295 are both synthetic analogs of growth hormone–releasing hormone (GHRH), the hypothalamic peptide that signals the pituitary to release growth hormone. They are frequently shelved next to each other, yet they are built on different fragments of GHRH and stabilized by entirely different chemical strategies. This article compares the two at the structural level — fragment length, the modification each one carries, and the persistence each shows in published pharmacology — using Sermorelin, the unmodified reference fragment, as the baseline.
The shared starting point: native GHRH
Endogenous human GHRH exists as a 44–amino acid peptide, GRF(1-44). The receptor-binding activity is concentrated in the front of the molecule: the first 29 residues, GRF(1-29), are the shortest segment that retains the parent hormone’s signaling activity. Both compounds in this comparison descend from that template, but they keep different amounts of it.
Native GHRH is short-lived. The principal reason is dipeptidyl peptidase-IV (DPP-IV), a plasma enzyme that cleaves the peptide between its second and third residues within minutes, inactivating it. Every stabilization strategy applied to a GHRH analog is, at its core, an attempt to defend against that cleavage. The two compounds solve the same problem in two different ways.
- Sermorelin is GRF(1-29) itself — the unmodified 29–residue fragment, with no protective modification, and correspondingly short-acting.
- Tesamorelin keeps the full 44–residue sequence and adds a chemical group to the N-terminus.
- CJC-1295 keeps the shorter 29–residue fragment and edits the sequence itself with several substitutions.
Tesamorelin: the full fragment with an N-terminal acyl group
Tesamorelin is a stabilized analog of the complete GRF(1-44) sequence — it retains all 44 amino acids of native GHRH rather than truncating to the 1-29 core. Its single defining modification sits at the front of the molecule.
That modification is a trans-3-hexenoic acid group — a short six-carbon acyl chain carrying a double bond — conjugated to the N-terminal tyrosine residue. In the FDA chemistry documentation and the published trial literature, the compound is described as the synthetic 44–amino acid GHRH sequence bearing a hexenoyl moiety attached at the amino terminus. Capping the N-terminus this way blocks the DPP-IV cleavage site, which is the structural feature responsible for the molecule resisting the enzymatic breakdown that rapidly clears unmodified GHRH.
The persistence this buys is modest in absolute terms. A population pharmacokinetic analysis pooling HIV-infected patients and healthy subjects characterized tesamorelin’s clearance and distribution, consistent with a short circulating half-life on the order of minutes rather than hours (González-Sales et al., Clin Pharmacokinet, 2015). The hexenoyl cap defends the front of the molecule but does not make it long-circulating. As for the GH axis: in a randomized, placebo-controlled trial in patients with HIV-associated abdominal fat accumulation, tesamorelin was measured to raise circulating insulin-like growth factor I (IGF-I) and to reduce visceral adipose tissue over 26 weeks relative to placebo (Falutz et al., N Engl J Med, 2007). That is what the trial measured in its research subjects; it is not a statement about any individual outcome.
CJC-1295: the short fragment with engineered substitutions
CJC-1295 takes the opposite approach. Rather than capping the full-length peptide, it works from the shorter GRF(1-29) core and rewrites part of the sequence. The backbone carries four amino acid substitutions, each chosen to blunt a specific route of enzymatic degradation — including a substitution at the position DPP-IV attacks. The result is a 29–residue analog that resists plasma degradation far better than the bare fragment.
This is where CJC-1295 splits into the two products commonly sold side by side:
- CJC-1295 No DAC is the stabilized GRF(1-29) backbone on its own — the four substitutions and nothing further. It is the same molecule the research literature often labels “Mod GRF 1-29.” It resists degradation but still clears on a timescale of minutes.
- CJC-1295 with DAC adds a second modification on top of that backbone: a Drug Affinity Complex (DAC), a maleimide-bearing group that bonds covalently to serum albumin in circulation. Tethered to that large, long-lived carrier protein, the peptide persists for days. We cover that mechanism in detail in our companion explainer on what DAC is.
The persistence difference between the two CJC-1295 forms is large and well characterized. In a clinical pharmacology study in healthy adults, a single administration of CJC-1295 with DAC was measured to elevate circulating growth hormone (GH) and IGF-I for several days, with an estimated half-life on the order of about a week (Teichman et al., J Clin Endocrinol Metab, 2006). A later study profiled the same GH/IGF-1 axis activation in healthy adult men one week after a single administration (Sackmann-Sala et al., Growth Horm IGF Res, 2009). Those are measurements in the studies’ research subjects, reported here as such.
Putting the two side by side
The comparison holds cleanly along three axes, with sermorelin anchoring the unmodified end:
- Fragment length: Tesamorelin retains the full GRF(1-44) sequence; CJC-1295 (both forms) and sermorelin are built on the shorter GRF(1-29) core.
- Modification type: Tesamorelin is capped with an N-terminal hexenoyl (trans-3-hexenoic acid) group. CJC-1295 instead edits the backbone with four amino acid substitutions, and the DAC version adds an albumin-binding maleimide group. Sermorelin carries no modification at all.
- Persistence (as published): Sermorelin, tesamorelin, and CJC-1295 No DAC all clear on a timescale of minutes; CJC-1295 with DAC persists for days because of the albumin tether (Teichman et al., 2006; González-Sales et al., 2015).
Read together, the family tells a tidy structural story: sermorelin is the unprotected fragment, tesamorelin protects the full-length peptide at one end, CJC-1295 No DAC protects the short fragment from the inside, and CJC-1295 with DAC layers a circulation-extending hook on top of that — siblings drawn from one hormone, separated by where and how each is reinforced.
Frequently asked questions
Are tesamorelin and CJC-1295 the same thing?
No. Both are synthetic GHRH analogs, but they are different molecules. Tesamorelin is the full 44–amino acid GRF(1-44) sequence with an N-terminal hexenoyl cap; CJC-1295 is built on the shorter 29–residue GRF(1-29) fragment with four amino acid substitutions, optionally plus a DAC group.
What is the main structural difference between them?
Fragment length and modification strategy. Tesamorelin keeps the whole GRF(1-44) chain and caps the N-terminus with a chemical group; CJC-1295 truncates to GRF(1-29) and substitutes amino acids within the sequence itself.
What is tesamorelin’s N-terminal modification?
It is a trans-3-hexenoic acid group — a short six-carbon acyl chain with a double bond — conjugated to the N-terminal tyrosine. This hexenoyl cap blocks the DPP-IV cleavage site, the structural reason the molecule resists the enzymatic breakdown that rapidly clears native GHRH.
How does CJC-1295 with DAC differ from CJC-1295 No DAC?
Both share the same stabilized GRF(1-29) backbone. The “with DAC” form carries an additional albumin-binding group, which published research associates with a half-life measured in days; the “No DAC” form lacks that group and clears within minutes. Our companion article on what DAC is walks through the mechanism.
Where does sermorelin fit in?
Sermorelin is the reference point: it is GRF(1-29) with no stabilizing modification at all. CJC-1295 is that same fragment reinforced, and tesamorelin is the longer fragment reinforced a different way. Comparing each analog back to sermorelin isolates exactly what its modification contributes.
Which one persists longer in published studies?
Among these compounds, CJC-1295 with DAC is the one published pharmacology associates with multi-day persistence, owing to its albumin tether (Teichman et al., 2006). Tesamorelin, CJC-1295 No DAC, and sermorelin all clear on a timescale of minutes (González-Sales et al., 2015).
References
- Falutz J, et al. Metabolic effects of a growth hormone-releasing factor in patients with HIV. New England Journal of Medicine. 2007. PMID: 18057338.
- González-Sales M, et al. Population pharmacokinetic analysis of tesamorelin in HIV-infected patients and healthy subjects. Clinical Pharmacokinetics. 2015. PMID: 25358450.
- Teichman SL, et al. Prolonged stimulation of growth hormone (GH) and insulin-like growth factor I secretion by CJC-1295, a long-acting analog of GH-releasing hormone, in healthy adults. Journal of Clinical Endocrinology & Metabolism. 2006. PMID: 16352683.
- Sackmann-Sala L, et al. Activation of the GH/IGF-1 axis by CJC-1295, a long-acting GHRH analog, results in serum protein profile changes in normal adult subjects. Growth Hormone & IGF Research. 2009. PMID: 19386527.
For research use only. The products and materials discussed are intended for laboratory research purposes and are not for human or veterinary use, diagnosis, or treatment. This article describes the chemical structure and published pharmacological research of a compound and does not constitute a claim of any effect in any individual.
