One of these three peptides is the active ingredient in an FDA-approved drug. One was approved, then discontinued. One missed the main goal of its trial. Yet sermorelin, tesamorelin and ipamorelin still get sold side by side as "the GH peptides," like three strengths of one thing. They aren't.
Two of them copy one signal. Ipamorelin mimics a different one.
Sermorelin and tesamorelin are both copies of GHRH, the brain's main "release growth hormone" signal. Ipamorelin mimics a different signal, ghrelin, and fits a different receptor (the lock on a cell that a signal has to fit). Same neighborhood. Different houses.
The proof: sermorelin vs tesamorelin vs ipamorelin, bead by bead
Let's get into it.
It all starts with a tumor. In 1982, Roger Guillemin's team pulled a 44-amino-acid peptide out of a pancreatic tumor that had caused acromegaly (a condition driven by too much growth hormone). It acted just like the brain's own release signal, which nobody had managed to isolate yet (Guillemin et al., Science 1982). Think of amino acids as beads on a string. That's 44 beads. The first 29 carry the full signal, so sermorelin is just those 29. Tesamorelin keeps all 44 and adds a small chemical cap to the front end (tesamorelin's FDA label).
The cap buys minutes, not days. An enzyme in the blood snips GHRH near its front end, and the cap blocks those scissors (Ferdinandi et al., 2007). In healthy men, sermorelin's 29-bead sequence had a half-life of about 4 minutes (Soule et al., JCEM 1994). Half-life is how long it takes for half of it to clear from the blood. Tesamorelin's label puts its half-life at 26 minutes in healthy people. Longer, sure. Nowhere near a week.
Ipamorelin isn't a GHRH copy at all. It's five beads long, built in the late 1990s for what's now called the ghrelin receptor, a separate lock. In pigs, it triggered growth hormone release without pushing up cortisol, a stress hormone its older cousins GHRP-6 and GHRP-2 did raise (Raun et al., Eur J Endocrinol 1998). That selectivity is what made it stand out.
So why should you care? They weigh completely different amounts. Ipamorelin is about 712 daltons (the unit chemists weigh molecules in). Sermorelin is about 3,358. Tesamorelin is about 5,136. The LC-MS identity test on a certificate of analysis (COA) is basically a molecular scale. If the name and the mass don't match, it's not a rounding error. It's a different molecule.
"But one is FDA approved, so they're all legit, right?" Nope. Tesamorelin's 2010 approval covers one prescription drug for one narrow use in adults with HIV. Research-grade tesamorelin isn't FDA approved. Sermorelin was discontinued in 2008, and the FDA later found that wasn't for safety or effectiveness reasons (Federal Register, 2013). Ipamorelin's published mid-stage trial didn't beat placebo, it was never approved, and the FDA notes serious adverse events, including a death, when it was given by IV (FDA). On our A-to-E evidence ladder, sermorelin and ipamorelin both sit at C. An approval belongs to one product. It doesn't rub off on the cousins.
The big learning lesson
Keep reading: CJC-1295 with DAC vs no DAC · Peptide half-life explained · How to read a peptide certificate of analysis
Frequently asked questions
What's the difference between sermorelin and tesamorelin?
Both copy GHRH. Sermorelin is its first 29 amino acids. Tesamorelin is all 44, plus a chemical cap that shields it from the enzyme that normally switches GHRH off.
What's the difference between sermorelin and ipamorelin?
They copy different signals and fit different receptors. Sermorelin is a GHRH copy. Ipamorelin is a five-amino-acid peptide that mimics ghrelin at the ghrelin receptor.
Is tesamorelin FDA approved?
Research-grade tesamorelin isn't. One prescription drug containing it was approved in 2010 for a single narrow use in adults with HIV. That approval doesn't extend to sermorelin or ipamorelin.