HGH and tesamorelin: what are the differences?

The HGH and the tesamorelin are often presented as two versions of the same subject. This is incorrect: one is growth hormone, the other is the signal that triggers it. This difference in level of action explains everything else.

The growth hormone axis, in three stages

Growth hormone production follows a cascade. The hypothalamus, at the base of the brain, releases GHRH (growth hormone releasing hormone). This orders the pituitary to secrete the growth hormone, which in turn acts on the tissues, largely through a second messenger produced by the liver, the IGF-1.

This cascade is regulated: when growth hormone and IGF-1 rise, the body itself slows down the following secretion, by a hormone called somatostatin. This is the point which fundamentally distinguishes the two molecules in question here.

HGH: the hormone itself

Human growth hormone is a protein of 191 amino acids, of approximately 22 kilodaltons, produced naturally by the pituitary gland. The so-called version recombinant is manufactured by biotechnology, from cells programmed to produce a protein with a sequence identical to the human hormone.

It is measured in international units (UI, or IU in English), a unit which expresses biological activity rather than a mass – a legacy of the time when the hormone was extracted from tissues, and where two batches did not have exactly the same activity.

Brought from outside, it no longer depends on the body's regulation: it bypasses the pituitary gland. This is what makes it a reference tool in experimental endocrinology, and also what makes it more difficult to study without disrupting the entire axis.

Tesamorelin: a signal, not a hormone

Tesamorelin takes over the 44 amino acids of human GHRH, with a chemical addition — a trans-3-hexenoyl group — which makes it more resistant to degradation by blood enzymes. Natural GHRH is destroyed within minutes; this stabilization is the entire reason for the existence of the molecule.

As it acts on the level above, the secretion it causes remains subject to the body's natural brakes: it retains the character pulsatile of physiological secretion, where a direct supply of hormone produces a continuous level. This is the difference that research most often highlights.

Tesamorelin is also one of the rare molecules in this family to have passed all stages of clinical trials: it has been authorized in the United States since 2010, under the name Egrifta, for a specific indication — lipodystrophy associated with HIV. This authorization concerns a medicine manufactured and controlled as such, not the vials sold as research peptides.

The differences at a glance

	HGH	Tesamorelin
Nature	Recombinant growth hormone	Analogue of GHRH
Size	191 amino acids (~22 kDa)	44 amino acids
Action level	Directly on fabrics	On the pituitary gland, upstream
Natural regulation	Bypassed	Preserved (pulsatile secretion)
Unit of measurement	UI (international units)	Milligrams
Medication status	Authorized in GH deficiency	Authorized in the United States (HIV)
Anti-doping list	Permanently banned	Permanently banned

What this changes for conservation

Both arrive in the form of freeze-dried powder, a state in which a peptide is stable for a long time protected from light. HGH, a much larger protein, is on the other hand more fragile once put back into solution: proteins of this size do not tolerate heat, vigorous stirring and freezing cycles. The subject is detailed in our guide on storage of lyophilized peptides.

Where does research stand?

Growth hormone has been studied since the 1950s and is one of the best documented proteins in endocrinology. Tesamorelin has solid clinical trials, but on a specific population and indication; outside of this framework, data remains limited.

Neither is authorized in France as a consumer product, and the vials sold here are intended exclusively for laboratory research. To check what a vial actually contains, the only valid document is the batch analysis report: our guide explains how to read a certificate of analysis.