Tesamorelin and ipamorelin both prompt the pituitary gland to release growth hormone, but they do it through two completely different “doors”. Tesamorelin is a long, modified copy of the body’s own growth hormone-releasing hormone (GHRH), while ipamorelin is a tiny five-amino-acid peptide that works on the ghrelin receptor. They also differ hugely in size, history and regulatory status.
If you have seen these two names side by side and wondered how they actually compare, this plain-English guide from Peptides UK walks through the differences without the jargon. It covers what each peptide is, how researchers think it works, where each one came from and what the rules say in 2026.
Tesamorelin vs ipamorelin at a glance
| Tesamorelin | Ipamorelin | |
|---|---|---|
| Peptide family | GHRH analogue | Growth hormone secretagogue (from the GHRP family) |
| Receptor it targets | GHRH receptor | Ghrelin receptor (GHS-R1a) |
| Length | 44 amino acids | 5 amino acids |
| Approximate molecular weight | About 5,136 Da | About 712 Da |
| Developed by | Theratechnologies (Canada) | Novo Nordisk (Denmark), first described in 1998 |
| Licensed medicine in the UK? | No | No |
| WADA status | Prohibited (S2) | Prohibited (S2) |
What is tesamorelin?
Your body makes a hormone in the brain called growth hormone-releasing hormone, or GHRH. Its job is to signal the pituitary gland to release growth hormone. Natural GHRH is 44 amino acids long, but it breaks down very quickly once it is in circulation.
Tesamorelin is a lab-made version of that same 44-amino-acid chain, with one extra tweak: a small chemical group (a trans-3-hexenoyl group) is attached to the start of the chain. That change helps protect it from the enzymes that normally chop GHRH apart. A 2009 review in Expert Opinion on Investigational Drugs describes its development as a synthetic GHRH analogue.
Because it copies a natural hormone, tesamorelin is often grouped with other GHRH analogues such as sermorelin and CJC-1295. If you are curious how it stacks up against its closest relative, our guide to sermorelin vs tesamorelin covers that comparison.
What is ipamorelin?
Ipamorelin is much smaller. It is a pentapeptide, meaning just five building blocks long, and it was created in the 1990s by scientists at Novo Nordisk who were working through a family of compounds called growth hormone-releasing peptides (GHRPs).
Rather than copying GHRH, ipamorelin acts on a different receptor: the growth hormone secretagogue receptor, better known as the ghrelin receptor. Ghrelin is often called the “hunger hormone”, but the same receptor also sits on cells in the pituitary.
The original 1998 paper by Raun and colleagues called ipamorelin “the first selective growth hormone secretagogue”. The headline finding was that, in animal studies, it released growth hormone without the rise in ACTH and cortisol seen with older peptides such as GHRP-6 and GHRP-2. That selectivity is the main reason it became so widely studied. For more background, see our ipamorelin research guide.
The key differences explained
1. Two different receptors
This is the big one. Think of the pituitary as having two separate switches that can both lead to growth hormone release. Tesamorelin presses the GHRH switch. Ipamorelin presses the ghrelin-receptor switch. Because the two pathways are separate, researchers study them both on their own and in combination, to understand how the body coordinates growth hormone signalling.
2. Size and structure
Tesamorelin is roughly seven times heavier than ipamorelin. At 44 amino acids it is a fairly large peptide, while ipamorelin’s five amino acids include some unusual, non-natural building blocks (such as Aib and D-2-naphthylalanine) chosen to make it more stable and selective. If you want a refresher on how amino acids join together in the first place, our explainer on what a peptide bond is is a quick read.
3. Natural copy vs designed molecule
Tesamorelin is essentially the body’s own hormone with a protective cap. Ipamorelin is a designed molecule: it does not resemble ghrelin closely, but it was engineered to fit the same receptor. That makes them interesting partners in research, as one shows what happens when you mimic a natural signal and the other shows what a purpose-built key can do.
4. Very different regulatory histories
Tesamorelin went through full clinical development. It was approved by the US Food and Drug Administration in 2010 as a prescription medicine for one narrow use in people with HIV. In Europe, the European Medicines Agency notes that the company applying for authorisation withdrew its application in 2012, so it was never authorised there. It is not a licensed medicine in the UK.
Ipamorelin, by contrast, has never been approved as a medicine by any major regulator. In the UK it sits in the same position as most research peptides: legal to buy as a research material, but not a licensed product.
Are tesamorelin and ipamorelin legal in the UK?
Neither peptide is a controlled drug under the Misuse of Drugs Act, so buying them for laboratory work is not a crime. Neither is a licensed UK medicine either, which means no one can legally sell or advertise them as a treatment. Our wider guide on whether peptides are legal in the UK explains how the MHRA draws that line.
Sport is a separate matter. The WADA Prohibited List bans GHRH analogues and growth hormone secretagogues under section S2, so both are prohibited in and out of competition.
Which one do researchers choose?
It depends entirely on the question being asked. A lab interested in the GHRH pathway, or in comparing modified versions of natural GHRH, would look at tesamorelin alongside sermorelin and CJC-1295. A lab interested in the ghrelin receptor, or in how selective a secretagogue can be, would look at ipamorelin alongside GHRP-2 and GHRP-6. Neither is “better”; they are tools for different jobs.
Whatever the project, quality matters. Look for a batch-specific certificate of analysis with HPLC purity and mass-spec identity results, clear research-only labelling and no health or dosing claims on the product page.
Where Peptides UK fits in
At Peptides UK we supply both tesamorelin and ipamorelin as lyophilised research powders, shipped from the UK. Every batch is HPLC & COA Verified, so you can check purity and identity before any lab work begins. We don’t give dosing, administration or human-use advice. Questions about a batch? Email research@peptideslabuk.co.uk.
Tesamorelin vs ipamorelin: FAQ
What is the main difference between tesamorelin and ipamorelin?
They act on different receptors. Tesamorelin is a modified version of growth hormone-releasing hormone (GHRH) and works on the GHRH receptor. Ipamorelin is a small five-amino-acid peptide that works on the ghrelin receptor, also called the growth hormone secretagogue receptor.
Is tesamorelin the same as sermorelin?
No. Both are GHRH analogues, but sermorelin is a shortened 29-amino-acid piece of GHRH, while tesamorelin is the full 44-amino-acid sequence with a small chemical group added to one end to make it more stable.
Is ipamorelin a GHRP?
Yes, in the broad sense. Ipamorelin was developed from the growth hormone-releasing peptide (GHRP) family and acts on the same receptor, but it was designed to be much more selective than older GHRPs such as GHRP-6.
Are tesamorelin and ipamorelin legal in the UK?
Neither is a controlled drug in the UK, and both can be bought as research materials. Neither is a licensed medicine in the UK, so neither can legally be sold or promoted as a treatment.
Are tesamorelin and ipamorelin banned in sport?
Yes. GHRH analogues and growth hormone secretagogues both fall under section S2 of the World Anti-Doping Agency Prohibited List, so both are banned at all times.
For laboratory research use only. Not for human or veterinary use. This article is general information, not medical or legal advice.
