Tesamorelin: The Capped Peptide That Wakes Up Growth Hormone

Some body fat sits right under the skin. You can pinch it. Other fat hides deep in the belly, like the part of an iceberg below the water. It packs in around the liver, the stomach and other organs.

In some people treated for HIV, that deep fat builds up. In 2010, the FDA approved the first medicine for it. It is a lab-made peptide called tesamorelin. Its clever trick is to wake up the body's own growth hormone.

What it is

A peptide is a short chain of amino acids. Think of amino acids as beads and a peptide as a short bead bracelet. New to this? Start with what a peptide is.

Your brain makes a peptide called GHRH. It tells the pituitary, a small gland under the brain, to let out growth hormone.

Tesamorelin is a lab-made copy of GHRH. It keeps all 44 beads. It adds one smart extra: a tiny chemical cap on the front end.

Think of the hard tip on a shoelace that keeps it from fraying. The cap helps shield the chain from an enzyme that snips natural GHRH and turns it off.

Its brand name is Egrifta. Its cousin CJC-1295 is another lab-made GHRH.

What it does in the body

A receptor is like a lock on a cell, and a peptide is the key. GHRH's lock sits on cells in the pituitary.

Tesamorelin fits that same lock. When it turns, the pituitary lets out its own growth hormone. It comes in bursts, like waves.

Growth hormone helps the body break down stored fat. It also tells the liver to make IGF-1, a helper hormone.

People with extra deep belly fat tend to make less growth hormone. Tesamorelin gives that system a nudge.

What scientists have found

In cells: In lab tests, tesamorelin switched on human GHRH locks about as well as the body's own GHRH.

In blood samples from rats, dogs and people, it broke down more slowly than natural GHRH. That is the cap at work.

In animals: In pigs, rats and dogs, it raised growth hormone and IGF-1 in the blood. In dogs given it for months, side effects were linked to very high growth hormone. They went away later.

In people: In 13 healthy men, two weeks of tesamorelin raised their own growth hormone at night. The bursts got bigger, and IGF-1 rose too.

The first big trial, published in 2007, had 412 people with HIV and extra belly fat. After 26 weeks, deep belly fat fell 15% on tesamorelin. On placebo, a dummy look-alike, it rose 5%.

A second trial, with 404 people, saw a drop too. Body weight barely changed. Fat on the torso went down, and lean mass, such as muscle, went up. When people later switched to placebo, the deep fat crept back.

A 2019 study enrolled 61 people with HIV and a fatty liver. They got tesamorelin or placebo for a year. Liver fat fell more on tesamorelin.

By the end, 35% of the tesamorelin group were below the fatty-liver line. On placebo, 4% were.

Liver scarring got worse in about 1 in 10 people on tesamorelin. On placebo, it was more than 1 in 3.

In a 2012 study of thinking, 152 adults aged 55 to 87 got tesamorelin or placebo for 20 weeks. Some had mild memory problems. The tesamorelin group did better on thinking tests, mainly ones on focus and switching tasks.

In the big trials, joint pain was a common side effect. So were redness or itching at the shot spot, pain in the arms or legs, swelling and muscle aches. Blood sugar can rise.

Where it stands

Tesamorelin has been an FDA-approved medicine since 2010. It is approved to reduce extra belly fat in adults with HIV and lipodystrophy. That is a change in where the body stores fat. It is not a weight-loss drug.

It came from a drug company in Montreal, Canada.

The World Anti-Doping Agency bans it in sport at all times.

The exciting next step is the liver. Researchers want to see if the liver and thinking results hold up in more people, over more time.

The bottom line

• Tesamorelin is a lab-made copy of GHRH, all 44 amino acids, plus a tiny cap that guards it.
• It wakes up the body's own growth hormone. In big trials in people with HIV, deep belly fat went down.
• FDA-approved since 2010, it is now one to watch for the liver.