What Is Ipamorelin?

Ipamorelin is a very small laboratory-made peptide, just five building blocks long, that fits a receptor on the pituitary gland and prompts it to release growth hormone. The receptor it fits is the one normally switched on by ghrelin, a hormone made mostly in the stomach. Ipamorelin is not approved as a medicine anywhere. It has been studied mainly in animals, and in people it reached one mid-stage trial, for a gut problem after surgery, where it did no better than a placebo.

Our page on growth hormone covers the hormone itself, and our page on CJC-1295 covers one way of asking the pituitary to release it. This page is about a second, separate way: a different door on the same gland. It also explains the word that appears in almost every description of ipamorelin, "selective", which means something narrower than it sounds.

A message to the pituitary

The pituitary gland is about the size of a pea and sits just under the brain. Among other jobs, it releases growth hormone in bursts, most of them during sleep. It does not decide on its own when to do this. It responds to messages.

Those messages arrive at receptors. A receptor is a structure on the surface of a cell shaped to catch one particular molecule. When the right molecule settles into it, the cell responds. Think of a receptor as a door with a very particular handle: only something shaped to fit that handle can open it.

The cells in the pituitary that make growth hormone have more than one such door. One is answered by growth hormone releasing hormone, a message from the brain just above. That is the door CJC-1295 is built to open. The other is the ghrelin receptor. Ipamorelin is built to open that one. Two doors, one room behind them, and both lead to growth hormone being released 4.

The lock that was found before the key

The ghrelin door has an unusual history, and it explains why ipamorelin exists at all.

In the late 1970s and 1980s, chemists made a series of small synthetic peptides that turned out to make animals release growth hormone. They were given the plain name growth hormone releasing peptides. Oddly, they did not work through the door everybody knew about. They were clearly opening some other door, but nobody knew what it was 4.

In 1996, researchers finally found it: a receptor in the pituitary and in the brain that these synthetic compounds switched on 2. For a few years it was what scientists call an orphan receptor, a lock with no known natural key. Your body would not build a door that nothing in the body opens, so something natural had to fit it.

In 1999 the natural key turned up, in a place few had expected: the stomach. Researchers found a hormone there that fitted the receptor and made the pituitary release growth hormone, and they named it ghrelin 3. Ghrelin is now best known as a hunger hormone, because its levels rise before meals, but its role in growth hormone release is how it was found.

So the history ran backwards. Chemists made keys, the keys revealed a lock, and the lock led to the body's own key. Ipamorelin is one of the later homemade keys, made in the 1990s with the benefit of everything learned from the earlier ones 1.

What exactly is ipamorelin?

It is a pentapeptide, which simply means a chain of five amino acids, the small building blocks that link together to make peptides and proteins. Several of its five are not the ordinary building blocks your body uses, which helps it resist being taken apart quickly. It is not a copy of ghrelin, which is a much longer chain. It is a small, separately designed molecule that happens to fit the same receptor 1.

Scientists call compounds like this growth hormone secretagogues. A secretagogue is anything that causes something else to be secreted, or released. Ipamorelin does not contain growth hormone and is not growth hormone. It asks the pituitary to release its own.

The name gives this away, if you know how to read it. Official drug names are often built from recognised endings that tell you which family a molecule belongs to, rather like a surname. Names ending in "-morelin" belong to the family of compounds that prompt growth hormone release through the ghrelin door. Ipamorelin has several cousins with the same ending, and the anti-doping list names a number of them side by side for exactly that reason 6. So when you meet an unfamiliar name ending in -morelin, you already know roughly which door it knocks on, even before you know anything else about it. You also know what it is not: none of them contain growth hormone itself.

What does "selective" mean?

The earlier homemade keys had a drawback. As well as growth hormone, they made the body release other hormones too. One was cortisol, often called the stress hormone, which is made by the adrenal glands and affects blood sugar, the immune system and much else. Another was prolactin, a pituitary hormone best known for its role in milk production. If you only wanted growth hormone to rise, those extra effects were unwanted noise.

When ipamorelin was first described, the researchers tested exactly this in animals. It raised growth hormone about as effectively as the earlier compounds, but it did not raise cortisol or its trigger hormone meaningfully, even when far larger amounts were given than were needed for the growth hormone response 1. That is where the word selective comes from, and the paper that introduced it called ipamorelin the first selective growth hormone secretagogue 1.

Here is the part that often gets lost. Selective is a comparison. It means ipamorelin moved fewer other hormones than the compounds that came before it, in the animals studied. It does not mean it acts only in the pituitary: ghrelin receptors are also found in the gut and the brain, which is why ipamorelin was later tested for a gut problem. And it does not mean the compound is harmless. Selectivity describes which hormones changed. Safety is a different question, and one that needs long studies in people to answer.

What has actually been studied in people?

Much less than its popularity suggests. The clearest published human study is a mid-stage trial in people who had just had part of their bowel removed. After this kind of surgery, the gut often goes quiet for days, a condition called postoperative ileus, and patients cannot eat normally until it wakes up. Because ghrelin receptors in the gut help drive its movement, the idea was that ipamorelin might speed that recovery 5.

The trial enrolled 117 patients, assigned by chance to ipamorelin or a placebo, an inactive look-alike, with neither patients nor doctors knowing who had which. It was well tolerated. But there were no significant differences between the two groups in the main measures, including how long it took before patients could manage a meal 5. In plain words, it did not show that it worked for that purpose.

That is an honest and useful result, and it should be read as one. A mid-stage trial is exactly where many promising ideas stop. It also means that the most rigorous human evidence for ipamorelin is a trial in which it did no better than placebo, for a use that has nothing to do with what it is usually discussed for today.

What has not been studied?

There are no large, long trials of ipamorelin in people for anything. There is no evidence from controlled human trials about body composition, recovery, sleep, ageing or athletic performance. And there is no long-term safety record.

It is also worth remembering a lesson from our page on growth hormone. Raising a hormone measurement is not the same as producing a benefit a person would notice. Even when growth hormone itself was given to healthy older adults in careful trials, the gains were small and the side effects real. A compound that prompts the body to release some growth hormone inherits that same gap between a number moving and a person being better off.

Where does it stand today?

Ipamorelin is not an approved medicine in the United States, the European Union or the United Kingdom, and no product containing it has been authorised for any use by those regulators. In sport, it is named on the World Anti-Doping Agency's prohibited list among growth hormone secretagogues, banned both in and out of competition 6.

What ipamorelin is not

• It is not growth hormone. It asks the pituitary to release the body's own.
• It is not ghrelin. It is a much smaller, separately designed molecule that fits the same receptor.
• It is not CJC-1295. That compound uses the other door, the one for growth hormone releasing hormone.
• It is not proven for anything in people. Its one published mid-stage trial did not beat placebo.
• It is not safe simply because it is selective. Selective describes which hormones moved in animal studies, nothing more.

The short version

Ipamorelin is a tiny homemade key for the pituitary's ghrelin door. It prompts growth hormone release, and in animals it did so without dragging cortisol along, which is all "selective" means. In people, its best trial was for a gut problem after surgery, and it did not beat placebo. Everything else said about it goes beyond what has been tested.