Best Peptides for Muscle Growth

Educational content only — not medical advice. Consult a licensed healthcare provider before starting, changing, or stopping any peptide protocol.

Overview

The phrase "best muscle building peptides" gets typed into search bars by lifters who have hit a wall, athletes chasing a plateau-breaker, and biohackers wondering whether a syringe of CJC-1295 will outperform another year of progressive overload. The honest answer sits between the hype videos and the dismissive forum posts, and it starts with an uncomfortable finding.

In a meta-analysis of 11 placebo-controlled trials in 254 healthy young subjects, growth hormone administration significantly increased lean body mass and decreased fat mass, and significantly increased anaerobic exercise capacity — but did not, over weeks to months, improve muscle strength (p = 0.36) or maximum oxygen uptake (p = 0.89) (PMID 28514721). The anaerobic-capacity finding is real and should not be buried, with one caveat the authors state themselves: it came from the only included study that measured it. That is exogenous GH itself, at supraphysiological exposure, in the population most peptide users resemble. Everything in the GH-secretagogue half of this page works upstream of that result. If GH does not make healthy young people stronger, a compound that raises your own GH is unlikely to do better.

That does not make the category worthless. Body composition changed in those trials, and body composition is what most people actually want. It does mean the honest pitch is "recomposition and recovery," not "strength."

Peptides for muscle growth are not steroids. They do not bind the androgen receptor, do not suppress the HPTA the way exogenous testosterone does, and — with the partial exception of IGF-1 LR3 — do not produce steroid-magnitude mass gains. What they do is act on specific pathways the body already uses: pulsatile GH release, IGF-1 signaling, satellite cell activation, and myostatin inhibition. If that distinction is new to you, Peptide 101: what are peptides? covers the chemistry before the pharmacology, and the beginner library collects the rest.

This pillar page is the central map for everything Peptides.NYC publishes on muscle and performance peptides:

• GH secretagogues — CJC-1295, ipamorelin, sermorelin, tesamorelin, hexarelin, MK-677
• The IGF-1 family — IGF-1 LR3, MGF, PEG-MGF
• Myostatin antagonists — Follistatin 344, ACE-031 (and why the latter's trial was stopped)
• Recovery peptides that support training volume — BPC-157, TB-500
• Body recomposition compounds — AOD-9604, 5-Amino-1MQ

The mechanism gap that matters

Steroids and muscle peptides act on different parts of the anabolic system. Anabolic-androgenic steroids work primarily through the androgen receptor, which is densely expressed in muscle and drives myofibrillar protein synthesis directly. Muscle peptides act through three mostly separate channels:

1. The somatotropic axis (GH → IGF-1). Secretagogues trigger pituitary GH release; GH's downstream effector is hepatic and local IGF-1. This system remains subject to somatostatin feedback, so it is self-limiting.
2. Satellite cell biology. IGF-1 LR3 and MGF act on satellite cells, the precursor pool that supplies new myonuclei — a slower, regenerative mechanism rather than a brute-force protein synthesis driver.
3. Myostatin and activin signaling. Follistatin and ACE-031 release a developmental brake. Effects in adults are smaller than in animal models or congenital cases, for reasons set out below.

None of those channels saturates the androgen receptor. That is the gap between peptide and steroid outcomes, and no peptide stack closes it.

Disclaimer: This content is for educational purposes only and is not medical advice. Muscle peptides discussed here are research compounds. Many are not FDA-approved for human use, essentially all are prohibited in tested sport, and some — notably IGF-1 LR3 and the myostatin inhibitors — carry serious concerns discussed below. Consult a licensed healthcare provider before starting any protocol.

The Muscle Peptide Families

Most lifters who try peptides get the available benefit from the secretagogue, recovery, and recomposition rows. The IGF-1 and myostatin rows are the ones with the serious unresolved questions.

GH Secretagogues — The Foundation

These compounds do not introduce exogenous GH. They act on the pituitary to release your own, and the two sub-classes do it by different receptors, which is the actual basis for stacking them.

What the human data shows

CJC-1295 is a long-acting GHRH analog. In two randomized, placebo-controlled, double-blind ascending-dose trials in healthy adults aged 21 to 61, a single subcutaneous injection produced dose-dependent increases in mean plasma GH of 2- to 10-fold for six days or more and in mean IGF-I of 1.5- to 3-fold for nine to eleven days, with an estimated half-life of 5.8 to 8.1 days. After multiple doses, mean IGF-I remained above baseline for up to 28 days, and the compound was described as safe and relatively well tolerated at 30 or 60 µg/kg (PMID 16352683).

One important detail the community version of this usually skips: that trial studied the long-acting, albumin-binding form — what is now sold as "CJC-1295 with DAC." Its 5.8-to-8.1-day half-life and 28-day IGF-I elevation are exactly the "GH bleed" profile people cite as the reason to prefer the short-acting "no DAC" version instead. The no-DAC version, which is the more popular purchase, does not have an equivalent published human pharmacokinetic study. So the strongest evidence in this class supports the form most of the community has decided not to use.

Ipamorelin is the pentapeptide Aib-His-D-2-Nal-D-Phe-Lys-NH2, developed as "the first selective growth hormone secretagogue." Its selectivity claim is well founded and specific: in swine, GHRP-6 and GHRP-2 both raised plasma ACTH and cortisol, while ipamorelin did not raise either above the levels seen with GHRH stimulation — and that held even at doses more than 200-fold above its ED50 for GH release. None of the secretagogues tested affected FSH, LH, prolactin, or TSH (PMID 9849822). That is animal work, but it is the direct source of the "ipamorelin is the clean GHRP" claim, and it holds up. Its dated FDA position sits on our tracker as ipamorelin.

MK-677 (ibutamoren) has the longest and best controlled dataset in the class, and it is more double-edged than the marketing suggests. In a two-year, double-blind, randomized, placebo-controlled trial in 65 healthy adults aged 60 to 81 — whose primary endpoints, fat-free mass and abdominal visceral fat, were assessed after one year — oral MK-677 25 mg daily raised GH and IGF-I into the young-adult range and increased fat-free mass by 1.1 kg versus a 0.5 kg loss on placebo (p < 0.001). But there was no significant difference in abdominal visceral fat or total fat mass, the increase in limb fat was greater on MK-677 (1.1 kg versus 0.24 kg, p = 0.001), body weight rose 2.7 kg versus 0.8 kg, fasting glucose rose by about 5 mg/dL (p = 0.015), and insulin sensitivity decreased (PMID 18981485).

One more finding from that trial matters more than any of the numbers above, and it is the authors' own: the study's power, in both duration and participant number, was insufficient to evaluate functional endpoints. Isokinetic strength, physical function and quality of life were measured as secondary endpoints, and the trial could not tell whether the extra 1.1 kg of fat-free mass did anything. The authors' conclusion calls for long-term functional studies, which is a polite way of saying the functional question is open (PMID 18981485).

Read that carefully if MK-677 is on your list. It increases lean mass at one year in a properly controlled trial — and it also adds limb fat, adds weight, measurably worsens glucose handling, and has not been shown to make anyone stronger or more functional. It is not a body-recomposition drug on that evidence. Its FDA position is a dated row on our tracker as MK-677.

Tesamorelin is the one FDA-approved compound in the class, for reduction of excess abdominal fat in HIV-associated lipodystrophy, and its approval and compounding position are dated on our tracker as tesamorelin. In a pooled analysis of two phase 3 trials (806 patients), 2 mg daily produced a −15.4% treatment effect on visceral adipose tissue at 26 weeks with no significant change in abdominal subcutaneous fat, and raised mean IGF-1 by 108 ng/mL (PMID 20554713).

Quick differentiation within the class

• CJC-1295 with DAC — the form with published human pharmacokinetics; long half-life, sustained IGF-I elevation rather than pulses.
• CJC-1295 no DAC — the popular short-acting form, chosen for pulsatility; no equivalent published human PK study.
• Sermorelin — the GHRH(1-29) fragment, very short-acting, available by prescription in the US.
• Tesamorelin — FDA-approved GHRH analog; the visceral-fat evidence above.
• Ipamorelin — the selective GHRP, with the ACTH/cortisol-sparing profile documented above.
• GHRP-2 / GHRP-6 — older ghrelin mimetics; both raised ACTH and cortisol in the swine comparison (PMID 9849822).
• Hexarelin — a strong acute GH releaser, but in healthy volunteers it decreased stage 4 sleep and EEG delta power while raising ACTH and cortisol (PMID 15177700) — worth knowing before adding it to a recovery-focused protocol.
• MK-677 — oral, long-acting, with the 1-year primary-endpoint data above including the insulin-sensitivity finding.

What the class does not do

The claim that GHRH + GHRP stacking is "synergistic" describes the receptor pharmacology, not a measured outcome — no trial has compared a GHRH analog plus a GHRP against either alone for body composition in healthy trainees. And per the GH meta-analysis at the top of this page, GH exposure did not improve muscle strength or VO2max in healthy young subjects, though it did significantly increase anaerobic exercise capacity in the single included study that measured that (PMID 28514721). Expect recovery and composition effects, and possibly something in short-burst work; do not expect your strength numbers to move because of the peptide.

• GH Secretagogue Protocol — every option in this class
• GH Peptide Stacking Guide
• Sermorelin Protocol · Ipamorelin Protocol · CJC-1295 Protocol · Tesamorelin Protocol · MK-677 Protocol · Hexarelin Protocol · GHRP-2 Protocol · GHRP-6 Protocol

IGF-1 LR3 — The Highest-Risk Compound on This Page

IGF-1 LR3 is an engineered IGF-1 analog: an arginine substitution at position 3 and a 13-amino-acid N-terminal extension, which together reduce binding to IGF binding proteins and greatly extend its circulating half-life relative to native IGF-1. That is why it is used, and it is also the whole of the risk.

No published human trial of IGF-1 LR3 for muscle growth exists. The dosing, the site-injection theory, and the cycle lengths circulating in the bodybuilding community are extrapolations. This page will not reproduce them; see the IGF-1 LR3 Protocol, which discusses what people do and where those numbers came from.

The cancer question, stated precisely

This is where vague language does the most damage, so here is what the largest human datasets actually found.

• Prostate. Pooled individual participant data from 12 prospective studies — 3,700 men with prostate cancer and 5,200 controls, with blood drawn on average five years before diagnosis — concluded that high circulating IGF-I concentrations are associated with a moderately increased risk of prostate cancer (PMID 18838726). A later individual-participant meta-analysis reached the same conclusion (PMID 26921328).
• Breast. Pooled individual data from 17 prospective studies in 12 countries, 4,790 cases and 9,428 matched controls, examined prediagnostic IGF-I and IGFBP-3 and breast cancer risk (PMID 20472501).
• Colorectal. The EPIC cohort plus a meta-analysis of prospective studies examined serum IGF-I, IGFBP-3, and colorectal cancer risk (PMID 19810099).

Three things follow. The association is real and has been found repeatedly in large prospective datasets, which is stronger than "some epidemiological signal." The magnitude described is moderate, not catastrophic. And critically, all of these studies measured endogenous IGF-I within the physiological range — none of them studied what happens when you inject an IGFBP-evading analog. Injecting IGF-1 LR3 is therefore not a scenario the epidemiology covers in either direction: it is off the end of the data, which is the opposite of reassuring.

Hypoglycemia is the acute risk, particularly when injected fasted or combined with insulin.

This is not a beginner compound and it is not a "let me try peptides" compound.

MGF / PEG-MGF — Localized Growth, Thin Evidence

MGF (mechano growth factor) is an alternatively spliced product of the IGF-1 gene — IGF-IEc in humans — expressed locally in response to mechanical loading and damage, and implicated in tissue repair and regeneration (PMID 20130113, PMID 20494600). In porcine satellite cells, MGF promoted proliferation and inhibited differentiation by downregulating key myogenic transcription factors (PMID 22875667) — which is the cell-level basis for the satellite-cell-recruitment story.

PEG-MGF is the pegylated version, which extends half-life enough to make subcutaneous administration practical.

The hyperplasia claim should be set aside. True muscle fiber hyperplasia in adult humans in response to MGF has not been demonstrated; the porcine work above shows proliferation and inhibited differentiation, which is not the same as new mature fibers. The site-injection strategy for bringing up lagging muscle groups is anecdote, confounded by simultaneous training, nutrition, and other compounds. No human trial of MGF or PEG-MGF for hypertrophy has been published.

• MGF / PEG-MGF Protocol

Follistatin 344 — Releasing the Brake

Myostatin is a TGF-beta family member that acts as a negative regulator of muscle growth. The demonstrations that this brake is real are striking and worth citing properly, because they are also the source of the most misleading analogy in this space.

Cattle. Double muscling in cattle is caused by mutations in the myostatin gene (PMID 9356471) — the Belgian Blue phenotype.

Humans. A child with gross muscle hypertrophy was found to carry a myostatin mutation, reported in the New England Journal of Medicine (PMID 15215484).

Now the caveat that matters more than either finding: those are lifetime, developmental absences of myostatin signalling, present from embryogenesis. They tell you what a body built without myostatin looks like. They tell you nothing about what happens when an adult with a fully developed musculature blocks a fraction of their myostatin for a few weeks. Using Belgian Blue cattle to market a peptide to adults is a category error, not evidence.

Follistatin 344 binds and neutralizes myostatin and activin. No published human trial of Follistatin 344 for muscle growth exists, the doses circulating in the community are extrapolated from animal work, and myostatin is expressed in cardiac tissue — which makes cardiac safety a legitimate open question rather than a scare story. Anyone considering it should have baseline cardiac imaging and be prepared to repeat it. No cycle lengths appear here because none of them come from a study.

• Follistatin 344 Protocol

ACE-031 — What Actually Happened

ACE-031 is a fusion protein of the activin receptor type IIB and IgG1-Fc, which binds myostatin and related ligands. Acceleron developed it for muscle-wasting diseases including Duchenne muscular dystrophy.

Here is the published record, which is more precise than the version told in forums. In a randomized, double-blind, placebo-controlled ascending-dose trial, ACE-031 was given subcutaneously every two to four weeks to ambulatory boys with DMD. The study was stopped after the second dosing regimen due to potential safety concerns of epistaxis and telangiectasias. The paper states ACE-031 "was not associated with serious or severe adverse events," and reports non-significant trends toward maintenance of six-minute walk distance, increased lean body mass and bone mineral density, and reduced fat mass. The authors' conclusion is that non-muscle-related adverse events contributed to the decision to discontinue, and that myostatin inhibition remains a promising therapeutic approach (PMID 27462804).

It was not the compound's only human study. An earlier double-blind, placebo-controlled single ascending-dose trial gave ACE-031 (0.02–3 mg/kg subcutaneously) or placebo to 48 healthy postmenopausal women. It was generally well tolerated, with injection site erythema among the adverse events, a mean half-life of 10 to 15 days, and at day 29 in the 3 mg/kg group statistically significant increases in total body lean mass (3.3%, p = 0.03 by DXA) and thigh muscle volume (5.1%, p = 0.03 by MRI) (PMID 23169607). That is the clearest human evidence on this page that myostatin pathway inhibition can add measurable muscle in people — from a single dose, in one month, in a population that was not trying to build any.

So: the DMD trial stopped early over nosebleeds and visible dilated skin vessels — findings consistent with off-target effects on activin/BMP signalling, which is involved in vascular endothelial maintenance — and the adverse events were not characterized as serious or severe. That is a meaningful distinction, and it cuts both ways. A sponsor halting a program over non-serious vascular findings is a strong signal about a pathway they did not understand well enough to dose safely. It is not the same as "the drug harmed people badly," and this page previously overstated it.

The lesson stands either way. When a sponsor with a development program walks away over a safety signal, that is the most credible safety review a compound in this space will ever receive. What is sold on gray-market sites today is unregulated reproduction of a molecule whose development program was abandoned — after it had shown, in the healthy-volunteer study above, that it does work. The protocol page exists as a warning, not an instruction manual.

• ACE-031 / Myostatin Inhibitor Protocol

Stack Structures, Without the Dosing Tables

No stack for muscle growth on this page has been tested as a stack in a human trial. The tiers below therefore describe structure and rationale; the amounts belong with a clinician and in the protocol guides, where they appear alongside their provenance.

Two structural points that are genuinely useful and do not require a dose:

• Add one compound at a time. You cannot attribute an effect or a side effect in a five-compound stack introduced simultaneously.
• Do not stack redundantly. Two ghrelin mimetics, or two GHRH analogs, act on the same receptor. That spends money on one pathway rather than layering two.

For the recomposition side, see the Fat Loss & Body Recomposition Protocol and the Fat Loss Hub. For the recovery side, see the Healing Hub. The two recovery compounds in the foundation tier get full treatment in the BPC-157 Complete Guide and the TB-500 Complete Guide, and are compared directly in BPC-157 vs TB-500.

Peptides vs Steroids — The Honest Comparison

The takeaway is narrower than the usual one. Peptides have a different side effect profile, not a uniformly cleaner one: the best-documented compound in the class measurably worsened insulin sensitivity at its 1-year primary endpoint, and was underpowered to show any functional benefit. And they pull on fewer anabolic levers. For someone who wants moderate, monitored body composition change, the category is reasonable. For someone who wants maximum mass, steroids will outperform — that is a description of pharmacology, not an endorsement.

Why Peptides Won't Replace Steroids for Mass

Three reasons, each tied to something on this page.

1. No androgen receptor saturation. The GH/IGF axis touches myofibrillar protein synthesis indirectly, and when GH exposure was tested directly in healthy young subjects it moved body composition without moving strength (PMID 28514721).
2. Endogenous regulation. Secretagogues still answer to somatostatin feedback. You still produce myostatin, and Follistatin blocks only part of it. Native IGF-1 is still buffered by binding proteins — the exception being IGF-1 LR3, which is precisely why it is the most steroid-like and the most concerning compound here.
3. The developmental analogy does not transfer. Myostatin-null cattle and the child in the NEJM report were built that way from the beginning (PMID 9356471, PMID 15215484). Adult, partial, short-term inhibition is a different proposition.

The specific "8–15 pounds of lean mass in 12 months" figure that used to appear here has been removed — it had no source, and the best-controlled study on this page reports a 1.1 kg fat-free mass gain at one year, which is considerably smaller than that.

For Specific Goals

Every row here is a community convention informed by the mechanism, not a trial-supported indication.

Bloodwork & Monitoring

If you take one practical thing from this hub, take this: these compounds require bloodwork, and the reason is documented rather than hypothetical. By the 1-year primary endpoint of the MK-677 trial, fasting glucose had risen and insulin sensitivity had fallen (PMID 18981485). Tesamorelin raised mean IGF-1 by 108 ng/mL in its phase 3 pool (PMID 20554713). Those are exactly the drifts you cannot feel.

A reasonable monitoring panel:

Frequency should be set with whoever orders the labs; the general principle is a baseline, a mid-cycle check rather than only an end-of-cycle one, and periodic rechecks on anything run long term. See the Bloodwork Checklist, and the safety library for the monitoring and side-effect material in more depth.

Side Effects & Safety

Commonly reported

Water retention (particularly MK-677 and the GHRPs), increased appetite (GHRP-6 and MK-677 are ghrelin mimetics, and appetite stimulation is the expected on-target effect), carpal-tunnel-type tingling or numbness from GH axis activation, injection site reactions, and headache or lethargy on GHRH analogs. Most of these come from user report; the controlled data is limited to what the trials above tabulated.

The documented and the serious

• Reduced insulin sensitivity. Not theoretical: measured at the 1-year primary endpoint of a 2-year trial of MK-677 25 mg daily, alongside a fasting glucose rise of about 5 mg/dL (PMID 18981485). Anyone with prediabetes or a family history should treat this as the main reason to monitor.
• IGF-1 and cancer. Circulating IGF-I is associated with moderately increased prostate cancer risk across 12 pooled prospective studies (PMID 18838726), with parallel analyses for breast (PMID 20472501) and colorectal cancer (PMID 19810099). Those studies measured endogenous levels; injecting an IGFBP-evading analog is outside their scope.
• Hypoglycemia with IGF-1 LR3, especially fasted.
• Vascular findings with activin-pathway inhibition. Epistaxis and telangiectasias stopped the ACE-031 trial in Duchenne muscular dystrophy (PMID 27462804). It was not the compound's only human study — an earlier single ascending-dose trial in healthy volunteers is described below.
• Sleep disruption with hexarelin, which decreased stage 4 sleep and delta power in healthy volunteers (PMID 15177700).

See the Peptide Safety Guide.

WADA Status — Critical for Tested Athletes

If you compete in any tested sport, treat this hub as informational only.

The World Anti-Doping Agency's Prohibited List includes growth hormone, its releasing factors and secretagogues (GHRH analogs, GHRPs and ghrelin mimetics), and IGF-1 and its analogs under the peptide hormones and growth factors class; agents modifying myostatin function under hormone and metabolic modulators; and any pharmacological substance with no current approval for human therapeutic use under the non-approved substances class — which is where compounds like BPC-157 sit. All of those classes are prohibited at all times, in and out of competition.

Check the current list yourself before relying on any of this. WADA republishes the Prohibited List annually and classifications change — wada-ama.org/en/prohibited-list. Two specific points worth knowing: BPC-157 being "not a steroid" does not make it permitted, and detection has moved well beyond looking for the parent compound — biomarker and biological-passport approaches target the downstream signature. The "they can't test for peptides" claim is long out of date.

Cycling Strategy

The specific week-counts that used to fill this section have been removed, because none of them derive from a study. What is available is this: the CJC-1295 pharmacokinetic work shows IGF-I remaining above baseline for up to 28 days after multiple doses (PMID 16352683), which is a real constraint on how quickly you can expect a washout; and the MK-677 trial dosed continuously across two years, assessing endpoints every six months with its primary endpoints at one year (PMID 18981485) — which is the closest thing to long-term data in the class, and still did not run long enough to answer the functional question.

The principles worth keeping:

1. Introduce compounds one at a time to establish tolerance and attribute effects.
2. Pull bloodwork mid-cycle, not only at the end. A mid-point IGF-1 and glucose check is how you catch a drift while it is cheap to fix.
3. Take deliberate off periods. Receptor desensitization in this class is argued more than demonstrated; the defensible reason is that an off period is the only way to see your own baseline.
4. Do not chain cycles indefinitely. The chronic risks on this page — glucose drift, sustained IGF-1 elevation — are functions of cumulative exposure.

See Peptide Cycling Strategies and the Peptide PCT Protocol.

Frequently Asked Questions: Muscle Peptides

Are peptides legal? It depends on the compound and the jurisdiction. Most muscle peptides in the US are sold as research chemicals and are not approved for human use, while sermorelin and tesamorelin are prescription drugs used off-label in this space. The 2026 regulatory picture has also moved for the compounding pathway — twelve peptides were removed from the FDA's 503A Category 2 do-not-compound list in April 2026 and an FDA advisory committee recommended six of seven peptides in July, but those recommendations are advisory only and none of the substances is on the 503A Bulks List. One compound central to this hub did not move, and the 503A/503B distinction matters here: ipamorelin acetate remains in Category 2 for 503B outsourcing-facility compounding as of the FDA list's April 22, 2026 revision (FDA). Its 503A Category 2 nomination was withdrawn in 2024, but it was never added to Category 1 either, so there is no lawful 503A pathway for it now. On that same revision the peptides still in Category 2 are GHRP-2, GHRP-6 and ipamorelin acetate for 503B, kisspeptin-10 for 503A, and ibutamoren mesylate — MK-677 — for both. None of this is legal advice.

Will peptides shut down my natural testosterone? HPTA suppression is not a described effect of the GH-axis compounds the way it is for exogenous androgens, and no trial on this page reported it. That is not the same as a guarantee of no endocrine effect, and it says nothing about what happens when these are stacked with testosterone. See the Peptide PCT Protocol.

Can I gain muscle on peptides alone, without training? Not meaningfully. GH administration increased lean body mass in placebo-controlled trials but did not improve strength, and the peptides here work upstream of GH. Without a training stimulus there is nothing for the signal to act on, and you would be accepting the metabolic risks for the smallest possible return.

How long until I see results? The controlled data gives you a sense of scale rather than a date. CJC-1295 raised IGF-I for nine to eleven days after a single dose, so axis activity shows up quickly on a blood test. Body composition is slower: the MK-677 trial measured its 1.1 kg fat-free mass difference over a year. Subjective sleep and recovery effects are what users report first, and those are user reports rather than trial endpoints.

Do peptides cause cancer? No trial has shown that a GH secretagogue causes cancer. The documented concern is specific to IGF-1: pooled analyses of prospective studies find higher circulating IGF-I associated with a moderately increased risk of prostate cancer, with parallel work in breast and colorectal cancer. Those studies measured naturally occurring levels, so they do not tell you what injecting an analog that evades IGF binding proteins does — which is a reason for caution, not reassurance.

What's the safest muscle peptide? Among compounds with actual human data, a selective GHRP such as ipamorelin has the cleanest documented endocrine profile: in the swine comparison it did not raise ACTH or cortisol even at very high multiples of its GH-releasing dose, whereas GHRP-2 and GHRP-6 did. "Safest with human data" is not the same as "safe," since none of these has long-term human safety follow-up except MK-677 — whose trial reported reduced insulin sensitivity and a roughly 5 mg/dL rise in fasting glucose alongside the lean-mass gain at its 1-year primary endpoint (PMID 18981485).

Can I stack muscle peptides with testosterone or steroids? This is common in the bodybuilding community, and it compounds the risks that matter most here — glucose handling, lipids, and cardiac load. No trial has evaluated the combination. If you are on TRT or using androgens, adding a GH- or IGF-axis compound is a decision for a physician who will run and interpret the bloodwork.

How do I know I'm getting real peptides? Batch-specific third-party certificates of analysis with HPLC and mass spectrometry, a vendor with a verifiable track record, and pricing that is not implausibly low. This matters more in this category than most, because the compounds with the highest risk are also the most expensive to make. See the Vendor Scorecard Framework and COA Reading Guide.

Do I need a doctor to do this? Practically, yes — not for permission but for the labs. The two documented harms on this page, reduced insulin sensitivity and sustained IGF-1 elevation, are both invisible without blood tests and both manageable if caught early. See the Compounding Pharmacy Guide and Doctor Conversation Script.

What happens when I stop? The axis returns to baseline, and the pharmacokinetics tell you roughly how fast: after multiple CJC-1295 doses, IGF-I stayed above baseline for up to 28 days. Composition gains hold to the extent that training and nutrition hold. No published study has followed what happens to lean mass after stopping any of these compounds in healthy trainees, so anything more specific than that is guesswork.

Featured Protocols on Peptides.NYC

• GH Secretagogue Protocol — CJC, ipamorelin, sermorelin, tesamorelin, MK-677
• GH Peptide Stacking Guide — combining GHRH and GHRP
• CJC-1295 Protocol · Ipamorelin Protocol · Sermorelin Protocol
• Tesamorelin Protocol · MK-677 Protocol · Hexarelin Protocol
• GHRP-2 Protocol · GHRP-6 Protocol
• IGF-1 LR3 Protocol — the highest-risk compound here, in detail
• MGF / PEG-MGF Protocol — localized growth and satellite cell theory
• Follistatin 344 Protocol — myostatin inhibition with appropriate caution
• ACE-031 / Myostatin Inhibitor Protocol — clinical history and why the trial stopped
• Fat Loss & Body Recomposition Protocol

Supporting content:

• BPC-157 Complete Guide · TB-500 Complete Guide
• Bloodwork Checklist · Peptide Cycling Strategies · Peptide PCT Protocol
• Beginners Stack Guide · Injection Safety Checklist
• Vendor Scorecard Framework · COA Reading Guide

Related Hubs

• Fat Loss Peptide Hub — the recomposition compounds and the incretin drugs
• Healing & Recovery Peptide Hub — BPC-157, TB-500, and MGF for repair
• Hormone Optimization Hub — the endocrine context for the GH axis
• Sleep Peptide Hub — why GH secretagogues are dosed before bed

Disclaimer: This content is for educational purposes only and is not medical advice. Muscle and performance peptides discussed on this page are research compounds; many are not FDA-approved for human use, several carry serious documented or unresolved concerns (particularly the IGF-1 family with respect to the cancer epidemiology cited above, and the myostatin antagonists with respect to cardiac and vascular safety), and essentially all are prohibited in tested sport. Consult a licensed healthcare provider before starting any protocol. Peptides.NYC does not sell peptides and does not provide medical advice.

Selected References

Every PMID linked above points to the PubMed record for that paper, so you can check the claim against the abstract yourself.

1. Hermansen K, Bengtsen M, Kjær M, et al. Impact of GH administration on athletic performance in healthy young adults: a systematic review and meta-analysis of placebo-controlled trials. Growth Hormone & IGF Research. 2017. PMID 28514721 · doi:10.1016/j.ghir.2017.05.005
2. Teichman SL, Neale A, Lawrence B, et al. Prolonged stimulation of growth hormone (GH) and insulin-like growth factor I secretion by CJC-1295, a long-acting analog of GH-releasing hormone, in healthy adults. Journal of Clinical Endocrinology and Metabolism. 2006. PMID 16352683 · doi:10.1210/jc.2005-1536
3. Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. European Journal of Endocrinology. 1998. PMID 9849822 · doi:10.1530/eje.0.1390552
4. Nass R, Pezzoli SS, Oliveri MC, et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Annals of Internal Medicine. 2008. PMID 18981485 · doi:10.7326/0003-4819-149-9-200811040-00003
5. Falutz J, Mamputu JC, Potvin D, et al. Effects of tesamorelin (TH9507), a growth hormone-releasing factor analog, in HIV-infected patients with excess abdominal fat: a pooled analysis of two multicenter, double-blind placebo-controlled phase 3 trials with safety extension data. Journal of Clinical Endocrinology and Metabolism. 2010. PMID 20554713 · doi:10.1210/jc.2010-0490
6. Frieboes RM, Antonijevic IA, Held K, et al. Hexarelin decreases slow-wave sleep and stimulates the secretion of GH, ACTH, cortisol and prolactin during sleep in healthy volunteers. Psychoneuroendocrinology. 2004. PMID 15177700 · doi:10.1016/S0306-4530(03)00152-5
7. Roddam AW, Allen NE, Appleby P, et al. Insulin-like growth factors, their binding proteins, and prostate cancer risk: analysis of individual patient data from 12 prospective studies. Annals of Internal Medicine. 2008. PMID 18838726 · doi:10.7326/0003-4819-149-7-200810070-00006
8. Travis RC, Appleby PN, Martin RM, et al. A meta-analysis of individual participant data reveals an association between circulating levels of IGF-I and prostate cancer risk. Cancer Research. 2016. PMID 26921328 · doi:10.1158/0008-5472.CAN-15-1551
9. Endogenous Hormones and Breast Cancer Collaborative Group; Key TJ, Appleby PN, et al. Insulin-like growth factor 1 (IGF1), IGF binding protein 3 (IGFBP3), and breast cancer risk: pooled individual data analysis of 17 prospective studies. Lancet Oncology. 2010. PMID 20472501 · doi:10.1016/S1470-2045(10)70095-4
10. Rinaldi S, Cleveland R, Norat T, et al. Serum levels of IGF-I, IGFBP-3 and colorectal cancer risk: results from the EPIC cohort, plus a meta-analysis of prospective studies. International Journal of Cancer. 2010. PMID 19810099 · doi:10.1002/ijc.24927
11. Matheny RW Jr, Nindl BC, Adamo ML. Minireview: mechano-growth factor: a putative product of IGF-I gene expression involved in tissue repair and regeneration. Endocrinology. 2010. PMID 20130113 · doi:10.1210/en.2009-1217
12. Dai Z, Wu F, Yeung EW, et al. IGF-IEc expression, regulation and biological function in different tissues. Growth Hormone & IGF Research. 2010. PMID 20494600 · doi:10.1016/j.ghir.2010.03.005
13. Qin LL, Li XK, Xu J, et al. Mechano growth factor (MGF) promotes proliferation and inhibits differentiation of porcine satellite cells (PSCs) by down-regulation of key myogenic transcriptional factors. Molecular and Cellular Biochemistry. 2012. PMID 22875667 · doi:10.1007/s11010-012-1413-9
14. McPherron AC, Lee SJ. Double muscling in cattle due to mutations in the myostatin gene. Proceedings of the National Academy of Sciences. 1997. PMID 9356471 · doi:10.1073/pnas.94.23.12457
15. Schuelke M, Wagner KR, Stolz LE, et al. Myostatin mutation associated with gross muscle hypertrophy in a child. New England Journal of Medicine. 2004. PMID 15215484 · doi:10.1056/NEJMoa040933
16. Campbell C, McMillan HJ, Mah JK, et al. Myostatin inhibitor ACE-031 treatment of ambulatory boys with Duchenne muscular dystrophy: results of a randomized, placebo-controlled clinical trial. Muscle & Nerve. 2017. PMID 27462804 · doi:10.1002/mus.25268
17. Attie KM, Borgstein NG, Yang Y, et al. A single ascending-dose study of muscle regulator ACE-031 in healthy volunteers. Muscle & Nerve. 2013. PMID 23169607 · doi:10.1002/mus.23539

Inclusion here is not endorsement — reference 1 is cited precisely because it is a null result for strength, and reference 4 because its data includes an adverse metabolic finding and was underpowered for function. Nothing on this page is medical advice.

Source: https://peptides.nyc/learn/goal/muscle