Peptides for muscle growth: what the research shows, doses and side effects

Search for peptides for muscle growth and you find the same short list of products. They fall into three groups. Growth hormone-releasing hormone (GHRH) analogues, such as CJC-1295, sermorelin and tesamorelin, copy the brain’s own signal for GH release. Ghrelin-receptor agonists, often called growth hormone secretagogues or GHRPs, include ipamorelin, GHRP-2, GHRP-6 and hexarelin; they act on a second receptor that also triggers GH release. The third group has one member on this page, IGF-1 LR3, an engineered copy of IGF-1 itself.

None of these is an anabolic steroid. They are chains of amino acids that act on hormone receptors, and none of them contains testosterone. They are marketed as muscle building peptides because of what they do to growth hormone and IGF-1, not because any trial has shown them to build muscle in healthy people. A 2026 endocrinology review of GH-axis peptides used without prescription sorted them into evidence tiers, from regulatory-grade randomised trials down to no human studies at all, and stressed how uncertain the claimed physique and performance benefits are ^[3].

This page is about that group. Other peptides are sold for injury repair rather than muscle size; they are covered in our pages on BPC-157 and TB-500 and the individual peptide guides.

Growth hormone is released from the pituitary in pulses. Two signals switch it on: GHRH from the hypothalamus and ghrelin, made mainly in the stomach. One signal, somatostatin, switches it off. GH then makes the liver and other tissues produce IGF-1, which drives growth and tissue building. The theory behind peptides for bodybuilding is that pushing this system harder, with more GH pulses or more IGF-1 activity, will add muscle.

The two releasing signals work together. In healthy men, a GHRP given with GHRH released more GH than the two would release separately ^[19], which is why a GHRH analogue and a ghrelin mimetic are often sold as a pair. Our page on CJC-1295 and ipamorelin covers the most common pairing, which has never been tested as a combination.

The weak link in the theory is the last step, from more GH to more muscle. It has been tested with growth hormone itself, and the result is the most important fact on this page.

A systematic review in the Annals of Internal Medicine pooled randomised trials that gave growth hormone to healthy, physically fit adults aged 13 to 45. It covered 27 study samples in which 303 people received GH, at an average of 36 µg/kg a day. Lean body mass rose by 2.1 kg more than in untreated participants, but strength and exercise capacity did not seem to improve, and people on GH more often had soft-tissue swelling (oedema) and fatigue. The authors concluded that claims that GH enhances physical performance are not supported by the scientific literature ^[1].

A training trial in young men shows where the extra lean mass went. Sixteen men aged 21 to 34 did 12 weeks of heavy resistance training while taking either GH at 40 µg/kg a day or a placebo. Fat-free mass and body water rose more in the GH group, but muscle size, strength and the rate of muscle protein building did not. The authors concluded that the extra lean mass was probably tissue other than skeletal muscle, and that GH did not add to the effect of training ^[2].

Two points follow for the peptides. First, lean body mass is not the same as muscle: it includes water, connective tissue and organs, and a rise on a scan can come from fluid. Second, the peptides are one step further away than GH itself. They can only ask the pituitary for more GH, which the body’s own brakes still limit, so there is no reason to expect a larger effect on muscle than injected GH produced.

Asked directly, what peptides are good for muscle growth has no evidence-based answer, because no peptide has been shown to increase muscle size or strength in healthy adults in a controlled trial. What exists is a mix of hormone studies in people, body-composition data in patient groups, and animal work. The sections below set out each group and say what kind of study each finding comes from.

Tesamorelin has by far the most human data of any peptide on this list. In a 26-week phase 3 trial of 412 people with HIV and excess abdominal fat, 2 mg a day raised IGF-1 by 81% on average and reduced visceral fat ^[12]. Across the phase 3 trials, lean body mass rose by about 1.2 to 1.3 kg more than on placebo ^[15], and a 2026 meta-analysis of five randomised trials confirmed an increase in lean body mass alongside the fat reduction ^[42]. A secondary analysis found that people whose visceral fat responded also gained trunk muscle area and lost fat inside the muscle ^[16]. These are small changes measured over six to twelve months in people with HIV, most of them men, and no trial has tested tesamorelin for muscle growth in healthy people or athletes.

Sermorelin’s adult evidence is two small studies in older men. Twice-daily injections of 0.5 or 1 mg for 14 days restored GH and IGF-1 to young-adult levels in 10 men ^[17]. A single 2 mg injection each night for six weeks in 11 men aged 64 to 76 raised night-time GH but changed neither IGF-1 nor body composition, weight or lipids; two of six strength measures and one endurance test improved ^[18]. There are no trials in younger adults.

CJC-1295 with DAC raised GH and IGF-1 for days after a single injection in healthy adults aged 21 to 61 ^[4], and the natural pulses of GH continued on top of a raised baseline ^[5]. Those studies measured hormones only. No study has measured muscle, strength or fat with CJC-1295, and the no-DAC form sold in most blends has no published human data at all.

The GHRPs reliably release GH in people, but the response tends to fade with repeated use, and the longer studies that looked for effects on the body found little. In nine healthy young men given 100 µg of GHRP-2 under the skin once a day, the GH peak fell from 83 µg/L on day 1 to 51 µg/L on day 5, and IGF-1 did not rise ^[21]. The only study of GHRP-2 in men seeking body-composition changes was a retrospective chart review of 14 men on testosterone who also took GHRP-2, GHRP-6 and sermorelin; average IGF-1 rose from 159.5 to 239.0 ng/mL, but lean mass and fat were not reported and there was no control group ^[22].

Hexarelin gives the clearest human answer in this group, and it is negative. Older adults injected 1.5 µg/kg twice daily for 16 weeks. IGF-1 did not change, and total body fat, lean body mass and bone density were not significantly different from baseline ^[24]. The GH response fell by about 45% over the same period, recovering within four weeks of stopping ^[25]. In rats given the chemotherapy drug cisplatin, hexarelin protected muscle mitochondria and reduced muscle wasting ^[28], an animal finding in a disease model, not in healthy muscle.

Ipamorelin has no human data on muscle. In rats given high-dose steroids, which break down muscle, ipamorelin neutralised the resulting negative nitrogen balance, though GH itself had a stronger effect ^[10], and in another rat study it counteracted a steroid-induced loss of muscle strength ^[11]. Neither study tested healthy animals. In normal mice, ipamorelin and GHRP-6 increased food intake and body fat through a route that did not depend on GH ^[9], and in rats GHRP-6 raised food intake and made fat pads 15 to 20% heavier ^[23]. For GHRP-6 there are no human trials measuring muscle mass, strength or performance.

IGF-1 LR3 was designed in Adelaide in the early 1990s as a laboratory tool. Its changes stop it binding well to the IGF-binding proteins that normally hold IGF-1 in reserve, which made it more potent than native IGF-1 in many cell experiments ^[29]. We found no published human trial of it.

The animal results are mixed. In rats made catabolic with the steroid dexamethasone, IGF-1 LR3 was about 2.5 times as potent as IGF-1 at improving weight gain and nitrogen retention ^[30]. In food-restricted rats it helped maintain body weight but did not preserve muscle protein, and in adult rats it increased muscle protein breakdown ^[31]. In finishing pigs, a four-day infusion of 180 µg/kg a day reduced weight gain and food intake and lowered the pigs’ own GH and IGF-1 ^[32]. None of this tells us what it does to muscle in people.

Many searches pair the two goals, asking for peptides for muscle growth and fat loss at the same time. GH does break down fat, and the best human data for any peptide here concern fat, not muscle. Tesamorelin reduced CT-measured visceral fat by 15.2% over 26 weeks in people with HIV, against a 5.0% rise on placebo ^[12]. A pooled analysis of both phase 3 trials, 806 patients in all, found no significant change in the fat under the skin that is visible in the mirror ^[13], and visceral fat came back once treatment stopped ^[14]. The US label describes tesamorelin’s effect on body weight as neutral and says it is not indicated for weight loss ^[15].

Outside HIV, one 20-week trial gave 1 mg of tesamorelin nightly to 152 adults aged 55 to 87, men and women, for cognition. Body fat fell by 7.4% on the GHRH analogue ^[45]. That was a secondary finding in older adults, not a body-composition trial.

For the ghrelin-receptor peptides the evidence runs the other way. Their main side effect is hunger, and in mice and rats ipamorelin and GHRP-6 added body fat ^[9][23]. So when people ask for the best peptides for muscle growth and fat loss, the honest answer is that the only one with trial evidence on fat is tesamorelin, in a specific patient group, and no peptide has trial evidence on muscle in healthy people. Our page on tesamorelin vs ipamorelin compares the two most-searched options directly.

Lists of the best peptides for muscle growth rank products by forum reputation. A ranking by evidence would need trials comparing the peptides with each other, or at least with placebo, on muscle size or strength in healthy people. None exists. What can be ranked is the amount of human evidence behind each peptide for any outcome: tesamorelin has phase 3 trials; sermorelin and GHRP-2 have paediatric and diagnostic studies; CJC-1295, ipamorelin, GHRP-6 and hexarelin have short hormone studies; and IGF-1 LR3 has none in people.

Before-and-after photos cannot fill the gap. They cannot show what a vial contained, and they usually coincide with changes in training, diet and often other drugs. A 2026 sports-medicine review discussed how the placebo effect, amplified by social media, shapes the perceived benefits of peptides ^[38].

Searches for the best peptides for female muscle growth run into a larger gap still. Most of the human data come from men. Tesamorelin’s phase 3 trials enrolled 86% and 84% men ^[15], the adult sermorelin studies were all in men ^[17][18], and the GHRP-2 chart review was in men on testosterone ^[22]. The 20-week tesamorelin cognition trial included women ^[45], but it did not measure muscle.

A study of online forums found that women using CJC-1295 described fat loss, muscle, skin and sleep among their reasons for using it ^[43], goals that no clinical study of CJC-1295 has tested. The tesamorelin label rules it out in pregnancy ^[15]. No peptide on this page has been studied for muscle in women.

Faster recovery between training sessions is another common claim. No human trial of any peptide on this page has measured recovery from exercise, muscle soreness or return of strength after training. The related animal data are from injury and disease models: steroid-treated rats for ipamorelin ^[10][11], chemotherapy-treated rats for hexarelin ^[28] and dystrophic mice for IGF-1 LR3.

Peptides for muscle recovery sold for tendon and soft-tissue injuries, such as BPC-157 and TB-500, work through different proposed mechanisms and have their own evidence gaps; see our page on BPC-157 and TB-500.

The doses below are those used in the cited studies, reported for information. They are not recommendations, most come from settings very different from bodybuilding, and animal doses cannot be converted into human ones.

GHRH analogues: tesamorelin was given at 2 mg under the skin once daily in the phase 3 trials ^[12] and 1 mg nightly in the older-adult trial ^[45]; the current US formulation is labelled at 1.28 mg daily ^[15]. Sermorelin was given at 0.5 or 1 mg twice daily for 14 days ^[17] and 2 mg nightly for six weeks ^[18] in older men. CJC-1295 with DAC was given as single or repeated injections of 30 to 90 µg/kg, weekly or less often, not daily ^[4][5].

Ghrelin-receptor agonists: GHRP-2 was given at 100 µg under the skin once daily for five days in healthy young men ^[21]. Hexarelin was given at 1.5 µg/kg under the skin twice daily for 16 weeks in older adults ^[24], and its GH response reached a plateau at about 1 µg/kg intravenously ^[27]. Ipamorelin’s human doses were intravenous infusions in a pharmacokinetic study ^[6] and 0.03 mg/kg twice daily in hospital after bowel surgery ^[7]; no subcutaneous human dose has been published. GHRP-6 human studies used single intravenous doses of 0.1 to 1.0 µg/kg ^[19].

IGF-1 LR3 has no human dose. The only IGF-1 dosing on a medicine label belongs to the different drug mecasermin, native IGF-1 given to children with severe IGF-1 deficiency under specialist care, within 20 minutes of a meal ^[34].

For the growth hormone comparison, the healthy-adult GH trials averaged 36 µg/kg a day for about 20 days ^[1]. Figures circulating online as bodybuilding protocols for any of these peptides do not come from the studies above. Our peptide calculator does the arithmetic of milligrams, millilitres and syringe units for a given vial, but it cannot make a dose appropriate or confirm what a vial contains.

Water retention and joint pain. Soft-tissue swelling was more common with GH in the healthy-adult trials ^[1], and the tesamorelin label lists fluid retention, joint pain, carpal tunnel syndrome, limb swelling and muscle pain ^[15]. Part of the lean-mass gain seen with GH-axis drugs may be this fluid ^[2].

Glucose and insulin. Raising GH works against insulin. In the tesamorelin trials, 5% of people developed diabetes against 1% on placebo, and 47% had IGF-1 more than two standard deviations above the normal range at 26 weeks ^[15]. The oral ghrelin mimetic MK-677 raised fasting glucose in healthy older adults ^[35]. A 2026 review lists blood-sugar disturbance among the adverse effects reported across the GH-axis peptides ^[3].

Appetite. Ghrelin-receptor agonists increase hunger. GHRP-2 raised food intake at a buffet meal by about 36% in healthy men ^[20], and GHRP-6 increased food intake in rats ^[23]; there is no equivalent controlled human study of GHRP-6, although hunger is the effect most associated with it. Ipamorelin increased food intake in mice ^[9].

Cortisol and prolactin. GHRP-2 and hexarelin raised prolactin, ACTH and cortisol in healthy volunteers, with an ACTH and cortisol response similar to that from corticotrophin-releasing hormone ^[26]. With hexarelin, cortisol rose by about 40% once the dose reached 0.5 µg/kg ^[27], and GHRP-6 roughly doubled prolactin and cortisol at its highest dose in men ^[19]. Ipamorelin did not raise cortisol in pigs ^[8], but that has not been confirmed in a human comparison.

Low blood sugar with IGF-1. IGF-1 acts like insulin. In pigs, IGF-1 LR3 lowered blood glucose more potently and for longer than native IGF-1 ^[33]. With the licensed IGF-1 medicine, 42% of children in trials had hypoglycaemia, some severe enough to cause seizures, and the label advises avoiding driving or exercise for 2 to 3 hours after a dose ^[34].

Cancer and the unknowns. Because GH and IGF-1 promote cell growth, tesamorelin is contraindicated in active cancer ^[15], and the 2026 review described growth-promoting concerns about these peptides as biologically plausible but unproven ^[3]. No peptide here has long-term safety data in healthy users. Supply adds its own risk: anti-doping laboratories have found glycine-modified GHRPs in seized products ^[40], altered growth-promoting peptides in black-market vials ^[39], and IGF-1 LR3 carrying a laboratory purification tag ^[41].

There is no evidence-based list of the safest peptides for muscle growth, because none has been tested for safety in healthy people using it for muscle. What the evidence can say is which peptides have the most safety data of any kind. Tesamorelin has a licensed label built on trials of more than 800 people over up to a year ^[13][15], though that safety profile applies to the licensed medicine under medical supervision, not to research vials. At the other end, IGF-1 LR3 has no human safety data at all, and the ghrelin-receptor agonists other than ipamorelin carry measured rises in cortisol and prolactin ^[26][27].

For unlicensed products, safety also depends on what is actually in the vial, which only an independent test can show. Our guide to third-party peptide testing explains what such tests check.

Every peptide on this page is banned in tested sport at all times, in and out of competition. The World Anti-Doping Agency’s Prohibited List names GHRH and its analogues, such as CJC-1295, sermorelin and tesamorelin, and growth hormone secretagogues and GH-releasing peptides, including ipamorelin, GHRP-2, GHRP-6 and hexarelin, under section S2.2.4 ^[36]. IGF-1 and its analogues, which covers IGF-1 LR3, are prohibited under section S2.3 ^[37].

The prohibition does not depend on whether a peptide works. Legal rules for buying and possessing these products differ by country and are covered on our legal status overview, including the UK and US pages.

Most peptides are broken down in the gut, so products sold as oral peptides for muscle growth deserve caution. Hexarelin shows the scale of the problem: taken by mouth it had about 0.3% of the GH-releasing activity of an intravenous dose, against about 77% under the skin ^[44]. The compound most often sold as an oral GH booster, MK-677 (ibutamoren), is not a peptide but a small molecule that acts on the ghrelin receptor. In a trial in 65 healthy older adults, 25 mg a day for up to two years raised fat-free mass by about 1.1 kg compared with placebo, but it also raised fasting glucose ^[35]. It has never been approved.

None of the injectable peptides on this page has a tested tablet, capsule or oral-drop form that has been shown to reach the blood in a useful amount.

PepFinder tracks listings for each of these peptides so they can be compared on a per-milligram basis: IGF-1 LR3 prices, CJC-1295 prices, ipamorelin prices, sermorelin prices, tesamorelin prices, GHRP-2 prices, GHRP-6 prices and hexarelin prices. Vial sizes vary, so the per-vial price is misleading; our note on how peptide prices work explains the comparison.

People searching where to buy peptides for muscle growth are buying research chemicals, not licensed medicines, whatever the label says. A certificate of analysis should name the peptide, its measured purity and the testing laboratory; our guide on how to read a peptide COA explains what to check, and our guide on how to spot a fake peptide supplier lists the warning signs. We also list third-party tested suppliers, and our methodology explains how suppliers are rated. None of this is a recommendation to buy or use any product.