Hexarelin: What the Human Studies Show, and Why It Is Not on FDA's Lists

Hexarelin is a synthetic six-amino-acid peptide that makes the pituitary release a large burst of growth hormone, and the human research on it is almost all from the 1990s and early 2000s. Those studies show a strong single-dose effect,^[10][11] a response that fades with repeated daily injections,^[16][18] a rise in prolactin of up to 180% and a cortisol rise similar to a standard CRH stimulation test,^[12][13] and a short-lived boost in heart pumping that does not seem to depend on growth hormone.^[22][25] No study has tested it for weight loss, and the longest adult trial, 16 weeks, found no change in body fat or lean mass.^[16] FDA has not approved it, it appears on none of FDA’s compounding lists, and no hexarelin study is registered on ClinicalTrials.gov.^[2][4][7]

What hexarelin is

Hexarelin belongs to a family called growth hormone-releasing peptides, or GHRPs. They are man-made, not natural hormones. They work on the same receptor as ghrelin, the hunger hormone made in the stomach, and that receptor on the pituitary triggers a pulse of growth hormone. Hexarelin is a modified version of an older compound, GHRP-6, built to be more stable. Its first human dose-finding study, run by the Italian company that developed it, gave 12 men single injections into a vein: the growth hormone peak rose with dose and was close to its maximum at 2 micrograms per kilogram.^[10]

It worked by several routes. Injected under the skin, it had about 77% of the activity of the same dose by vein. By nasal spray the figure was 4.8%, and by mouth 0.3%, so oral doses had to be thousands of times larger.^[11] At the same dose by vein, hexarelin released about twice as much growth hormone as GHRH, the body’s own releasing hormone.^[11] It goes by another name, examorelin, which is how the World Anti-Doping Agency lists it.^[6]

Hexarelin also binds a second target. Researchers in Montreal found that in rat hearts it attaches to CD36, a receptor on heart muscle and blood-vessel cells better known for taking up fats and oxidized cholesterol.^[26] That binding is the basis of claims that hexarelin protects the heart. The same paper also showed something sellers leave out: activating CD36 with hexarelin narrowed the coronary arteries in isolated hearts, and the authors suggested CD36 may play a part in coronary spasm.^[26]

The hexarelin evidence in people, sorted by what was tested

The main problem: the response fades with daily use

The longest adult study gave hexarelin under the skin twice a day for 16 weeks, at 1.5 micrograms per kilogram, and tested the growth hormone response to a single dose along the way. The area under the growth hormone curve fell from 19.1 at the start to 12.3 at week 4 and 10.5 at week 16, roughly a 45% drop. Four weeks after stopping, it was back to 19.4.^[16] The authors called this a partial and reversible loss of response. Over the same 16 weeks, IGF-1, the hormone that carries most of growth hormone’s effects on tissue, did not change, and neither did body fat, lean mass or bone density.^[16] The authors judged the biological impact on the growth hormone system to be minimal.

Children showed the same pattern. In seven short children given hexarelin nasal spray three times a day, the peak growth hormone response to a test dose fell from 70.6 to 34.1 units after one week and stayed near that level for six months. A test dose by vein dropped further, from 84.8 to 19.8 units, by the end of treatment.^[18] Even a single day of two or three injections blunted the response to a later IV dose in healthy young men.^[20]

One study pointed the other way. Elderly volunteers who took hexarelin by nasal spray for 8 days or by mouth for 15 days kept their growth hormone response, and IGF-1 rose slightly with the oral form.^[19] Those courses were short and used low-absorption routes. The weight of the evidence is that daily injections lose part of their effect within weeks. A vendor protocol that cycles hexarelin on and off is a reaction to this problem; it has not been tested.

Cortisol and prolactin

Hexarelin is not selective for growth hormone. A single IV dose raises prolactin and the stress-hormone pair ACTH and cortisol. In healthy adults, the cortisol rise after hexarelin was similar to the rise after a standard CRH stimulation test.^[13][14] In a dose-response study, prolactin rose by up to 180% from baseline and cortisol by about 40% once the dose reached 0.5 micrograms per kilogram.^[12] In people with Cushing’s disease, a pituitary tumor that overproduces ACTH, hexarelin’s ACTH rise was about seven times larger than CRH’s.^[13] In young men who took four small doses in the evening, deep sleep fell and growth hormone, prolactin, ACTH and cortisol rose overnight.^[28] That runs against marketing that lists better sleep among hexarelin’s benefits.

These rises were short, and with repeated dosing they did not build up. After 16 weeks of twice-daily injections, the cortisol response to a dose was lower than at the start, prolactin was unchanged, and 24-hour urine cortisol did not move.^[17] Single-day studies found the same.^[20] The studies are small and supervised. They do not tell anyone how a vendor product at an unverified dose, stacked with other peptides, behaves over months.

Hexarelin vs ipamorelin

Ipamorelin is the peptide most often set against hexarelin, and it is sold on the claim that it is the “clean” one. That claim comes from Novo Nordisk’s 1998 paper describing ipamorelin as the first selective growth hormone secretagogue. GHRP-2 and GHRP-6 raised ACTH and cortisol; ipamorelin did not, even at doses more than 200 times its effective dose.^[30] The selectivity tests in that paper were done in pigs. The published human study of ipamorelin modeled its blood levels and growth hormone response in healthy men and did not report cortisol or prolactin.^[31] No published study has compared hexarelin and ipamorelin head to head in people.

Compared fairly, hexarelin has more human data, and that data shows the cortisol, prolactin and fading-response problems directly. Ipamorelin’s cleaner profile is an animal finding that was never confirmed in a published human hormone panel. Neither has been shown to change weight, fat or muscle in people. Our CJC-1295 and ipamorelin review sets out what FDA has written about ipamorelin and the stack it is usually sold in.

Hexarelin and the heart

The heart findings are the most distinctive part of the hexarelin record. In seven healthy men, a single IV dose raised left ventricular ejection fraction, the share of blood the heart pumps out with each beat, from 64.0% to 70.7%. A dose of growth hormone that produced the same growth hormone levels did nothing to the heart.^[22] In men with severe growth hormone deficiency, whose growth hormone barely rose, ejection fraction still went up.^[23] In 24 men having bypass surgery, hexarelin raised ejection fraction and cardiac output within 10 minutes and for up to 90 minutes, while GHRH, growth hormone and placebo had no effect. Blood pressure also rose.^[25]

The effect did not hold in every heart. In patients with ischemic cardiomyopathy, ejection fraction rose from 22.6% to 26.2%; in patients with dilated cardiomyopathy it did not change.^[24] In rats after a heart attack, two weeks of hexarelin improved pumping about as much as growth hormone did.^[27] Every human study was a single dose, watched for an hour or two. There is no human trial of repeated hexarelin for heart failure or any heart condition, and the CD36 work in rat hearts showed coronary narrowing as well as benefit.^[26] A seller who calls hexarelin cardioprotective is extending a few one-hour scans into a claim nobody has tested.

Hexarelin and weight loss: no human evidence

Growth hormone breaks down fat, and that is the whole case sellers make for hexarelin as a fat-loss peptide. The human data do not support it. The 16-week adult study measured body composition and found no change in total body fat or lean mass.^[16] In children with obesity, hexarelin’s growth hormone response was smaller than in other children.^[15] In short children treated for months, skinfold thickness fell while weight rose, which reflects growth rather than weight loss.^[21]

The fat-loss evidence is from mice. In lean, insulin-resistant mice, 12 days of hexarelin lowered fat mass and raised lean mass, although the mice ate more and their total weight did not change.^[33] In obese mice missing the MC4R appetite gene, a continuous pump of hexarelin for three to four weeks cut visceral and liver fat, with food intake held equal.^[34] Neither study has been repeated in people. No hexarelin study of any kind is registered on ClinicalTrials.gov.^[7]

There is no evidence on hexarelin taken with a GLP-1 drug. There is one reason for caution for anyone on semaglutide or tirzepatide for diabetes: reviews of the growth hormone secretagogue class flag rises in blood sugar from reduced insulin sensitivity.^[35][36] Hexarelin’s own effect on glucose in long-term use was not measured in the studies above. Our peptide menu review counts the human trials behind each peptide sold beside GLP-1s.

Is hexarelin legal? FDA status

No hexarelin product is approved by FDA. FDA’s drug-approval database and the DailyMed label library return no match for it. The only drug acting on this receptor that appears on DailyMed is macimorelin, sold as Macrilen, an oral solution approved to diagnose adult growth hormone deficiency, not to treat anything.^[8]

That leaves compounding. A pharmacy compounding under section 503A may use a bulk ingredient only if it meets a USP or NF monograph, is a component of an FDA-approved drug, or is on FDA’s 503A bulks list.^[3] Hexarelin is not a component of any approved drug, and the 503A bulks list in federal regulation names six substances, none of them a peptide.^[4] While FDA works through nominated ingredients, it tolerates compounding with substances in its interim Category 1, under conditions.^[3] Hexarelin is not in Category 1. It does not appear anywhere on FDA’s 503A category lists, its 503B category lists or its page of substances that raise safety risks.^[1][2][5]

That absence is not a clean bill of health. It means nobody put hexarelin through FDA’s nomination process, so FDA has never evaluated it. Its close relatives have been evaluated. GHRP-2 and GHRP-6 sit in Category 2 for outsourcing facilities, the significant-safety-risk category, and in Category 3 for 503A pharmacies. For GHRP-2, FDA cites reports of serious adverse events, including a higher insulin requirement and pancreatitis, though causality was not established.^[1][2]

Our peptide legal-status guide sets these lists out for every peptide FDA has named, and the peptide status checker looks one up. 503A vs 503B pharmacies explains the two compounding channels.

Hexarelin as a research peptide

Most hexarelin is sold online in vials labeled “for research use only,” and at least one telehealth clinic in our register lists it on its peptide menu beside compounded GLP-1s. A 2026 review of growth hormone peptides used without a prescription lists hexarelin among them and catalogs the problems clinicians see: raised prolactin and cortisol, appetite changes, blood-sugar problems, fluid retention, joint and muscle pain and injection-site reactions, on top of uncertainty about what is in the vial.^[36]

The research-use label does not change the legal picture. In a December 2024 warning letter to a peptide seller, FDA said that despite “RESEARCH USE ONLY” labels, the seller’s websites showed its products were “intended to be drugs for human use.”^[9] That letter concerned GLP-1 products; the same issues are covered in buying tirzepatide as a research chemical. To judge a vial’s purity claims, see how to read a peptide certificate of analysis.

Where hexarelin fits among growth hormone peptides

Hexarelin was once a candidate diagnostic: in 19 patients with pituitary disease, a low growth hormone response to hexarelin tracked the gold-standard insulin tolerance test, though it was a poor test of cortisol reserve.^[29] That role went to macimorelin, which did reach approval.^[8] Two other growth hormone peptides have real approval histories. Sermorelin was approved for children with growth hormone deficiency and later discontinued for reasons FDA recorded as unrelated to safety, and tesamorelin is approved to reduce abdominal fat in adults with HIV, with a label that says it is not for weight loss. Hexarelin has neither kind of record. For the oral secretagogue sold for the same reasons, see MK-677, and for another hormone-axis peptide with more human data than its marketing suggests, kisspeptin.