Growth hormone peptides promise to stall aging—but does the science stack up?

This is the injectables age. With more than one in 10 Americans now taking GLP-1 weight-loss drugs and some of us branching out to various other peptides, we have as a society seemingly gotten very comfortable with injections that modify our bodies. After all, why wouldn’t someone want to take one that could boost their fitness recovery, combat aging, curb hunger and trigger fat loss?These are the claims made by proponents of injectable peptides that promise to stimulate the body’s levels of growth hormone. But what evidence is there? And should we be trying to produce more growth hormone at all?Growth hormone is a small protein made by the brain’s pituitary gland, and it is released in pulses day and night, explains Brad Anawalt, an endocrinologist at the University of Washington School of Medicine. In children and young adults, it does what the name suggests, lengthening bones and helping bodies grow. Levels of the hormone peak in puberty and then decline by as much as half every seven to 10 years after that.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.In adults, the hormone plays a role in blood sugar control, bone density and muscle growth. But the big drop in levels with age is the entire premise behind growth hormone peptides. Prodding the pituitary to release more growth hormone, proponents say, can defy aging. Podcaster Andrew Huberman, health coach Christian Poulos and wellness author Mark Hyman are all fans its supposed power over our bodies, to name just a few.Substances such as sermorelin, tesamorelin, CJC-1295, ipamorelin and a suite of other formulas are reaching more people through compounding pharmacies, telehealth prescribers and longevity clinics. These sellers often claim that the compounds can increase muscle mass and reverse aging by inducing “natural” levels of the hormone. But experts say the science to support these ideas is thin, and the risks are serious.“Anytime you have something that changes with age, particularly if it decreases, people say well, that must be why you age,” says Anne Cappola, an endocrinologist at the University of Pennsylvania. As a result, people put two and two together, she muses. “If you take growth hormone, then you may not age.” But the reality isn’t so simple.Complicating matters are that two of the most popular growth hormone compounds—sermorelin and tesamorelin—were created with specific people in mind.Sermorelin was approved by the U.S. Food and Drug Administration in 1997 to treat growth hormone deficiency in children, but it was discontinued in 2008 and eventually withdrawn by the FDA for commercial reasons. Given that history, “we know that it will raise growth hormone levels,” says Alexander Pastuszak, a urologist and men’s health researcher at the University of Utah School of Medicine. But there are no large-scale randomized controlled trials in healthy adults to test for performance, body composition, or longevity, he says.In other words, we don’t really know what taking sermorelin does to adult bodies, because we’ve never thoroughly tested for that.Tesamorelin, meanwhile, was approved in 2010 by the FDA to treat people with HIV-associated lipodystrophy, which causes abnormal fat buildup in some areas of the body and fat loss in others. In a trial of more than 400 people with the disease, visceral fat—the kind that packs around internal organs and is known to raise the risk of chronic diseases and premature death—fell by about 15 percent in people taking the drug. Importantly, the goal of the medication “was to reduce fat tissue, not muscle growth,” Pastuszak says. And again, the evidence for it comes from a very specific population—unlikely the same people in search of peptides to enhance physical performance or longevity, he says.Other popular compounds available online, such as CJC-1295, ipamorelin, GHRP-2 and GHRP-6, have never been approved by the FDA. There is evidence these compounds raise growth hormone levels, but there is no solid proof that they have any effect on muscle and fat.Complicating matters once more is the fact that these substances are rarely taken alone. Peptides are typically “stacked,” meaning a person is likely taking several at a time, which makes it harder to tease out what any single peptide is doing.Evidence for growth hormone itself is more promising. One review found that more than 200 older adults saw about a 4.6-pound increase in lean body mass, and a similar decrease in fat mass, when taking growth hormone. But these effects were accompanied by swelling, joint pain, carpal tunnel and, in some cases, diabetes. In other words, growth hormone boosted the participants’ muscle mass, but it didn’t restore or improve their mobility. “We want them to walk better, move around, and get out of bed or out of a chair,” Cappola says. On those measures, the drug didn’t deliver.“Lean body mass” describes everything in the body that’s not fat—including muscle but also water and organs. “What you really want is function,” Cappola says. “How well does [the muscle] work, how strong are you—not how big the muscle is.”Other results are murkier. Older people taking growth hormone as well as doing strength training or taking sex steroids don’t see an additional increase in strength. Young, fit adults taking growth hormone gain muscle mass, but again, they don’t get stronger. In one study in athletes, for example, growth hormone raised sprint capacity on a stationary bike by about 4 percent, and the effect disappeared after stopping the treatment. That’s a tiny gain—enough for the World Anti-Doping Agency to ban growth hormone and substances that boost its production in competitive sports, but not enough for your average gym-goer to notice at all.Peptide proponents claim that prompting your own pituitary to release growth hormone is “natural,” but some gruesome side effects suggest otherwise. In his own practice, Pastuszak describes seeing joint pain as bones “start to grow and push out beyond their limits.” This is a sign of a condition called acromegaly, in which an adult has too much growth hormone.“You don’t get taller, but your hands and feet get bigger,” Anawalt says. “And it causes heart disease, increased risk of stroke, increased risk of colon cancer.”Those risks need to be considered before accounting for what else might be in the vial. A recent analysis, which has not yet been peer-reviewed, found that between about 40 and 70 percent of thousands of gray-market peptide samples tested—including sermorelin, tesamorelin, CJC-1295 and ipamorelin—failed to meet basic quality criteria. About 15 percent of a subset of the products tested contained measurable levels of endotoxin, a sign of bacterial contamination during manufacture. The dangers rise with injections, Cappola says. Swallow something contaminated and you might vomit it back up, she says, but an injection goes straight into the bloodstream.When Anawalt’s patients ask him about peptides, he spends time trying to understand what they want to change. Usually, he says, they want to be more attractive. There are safer alternatives with a more solid evidence base—such as creatine. With regular weight training, it can slightly improve performance, but “it’s not going to turn you into Ryan Gosling.”“There’s a lot of interest in magic, in doing things that involve natural substances and diets and so forth,” Anawalt says. “Believe me, if I thought a peptide was going to work, I would recommend it.”