Muscle peptides is an everyday name for several molecules that either target the same pathways as growth hormone and IGF-1, or try to block myostatin, the protein that limits muscle growth. The group covers IGF-1 LR3, DES(1-3) IGF-1, MGF and PEG-MGF, along with follistatin and ACE-031.
They share one thing: the mechanism sounds promising and human data are close to non-existent. None of these molecules is approved for building muscle, and the research programme for one of them was closed on safety grounds. This article sets them out on one map.
What is the IGF-1 axis and why is it targeted?
IGF-1 is a growth factor which, once bound to its receptor, activates the PI3K, Akt and mTOR pathway. That pathway increases muscle protein synthesis, curbs protein breakdown by blocking FOXO proteins, and stimulates satellite cells involved in building muscle fibres.
IGF-1 LR3 is a modified analogue of IGF-1, designed to bind more weakly to carrier proteins and so remain active for longer. MGF and PEG-MGF are related molecules from the same axis, with the pegylated version intended to survive longer in circulation.
What is myostatin and how do its blockers work?
Myostatin, also known as GDF-8, is a protein that limits muscle growth. Molecules described as myostatin blockers try to switch off that brake.
Follistatin is a protein that binds ligands of the TGF-beta superfamily, myostatin among them, and thereby lifts the limit on growth. ACE-031 is a fusion protein based on the activin receptor type 2B, acting as a decoy receptor that captures myostatin and related molecules before they reach cells.
What do human studies show?
For IGF-1 LR3 no human pharmacokinetic study has been published. Everything known about how it is broken down and distributed comes from rodent models. Data on efficacy and safety in muscle applications are missing as well.
For follistatin there are no randomised human trials on muscle mass. The striking results used to advertise it come from mice lacking the myostatin gene, and those animals have different muscle physiology from animals and people with a working gene.
ACE-031 was studied in boys with Duchenne muscular dystrophy. The trials were halted on 21 April 2011 on safety grounds, and on 2 May 2013 the companies closed the programme without restarting it. Some participants developed nosebleeds and bleeding gums, along with small dilated blood vessels in the skin, which resolved after the drug was stopped.
What are the risks of these peptides?
For IGF-1 LR3 the risks listed include hypoglycaemia, a drop in blood sugar, and suppression of the body’s own growth hormone and IGF-1 axis through feedback in the hypothalamus and pituitary, described in animals.
For ACE-031 the vascular effects were linked to blocking BMP9 and BMP10 signals, which matter for normal blood vessel function. That is the reason a programme with clear efficacy signals was nevertheless closed.
What is the legal and sporting status?
None of these molecules is approved for building muscle or improving athletic performance. IGF-1 LR3 appears on the World Anti-Doping Agency list in category S2 and is prohibited at all times, in and out of competition.
In our shop they appear as research material: IGF-1 LR3, MGF, follistatin 344 and ACE-031. The cart and the checkout are in English and prices are shown in Polish zloty. Peptides acting on the growth hormone axis itself are covered in the article on growth hormone peptides.
Frequently asked questions
Does IGF-1 LR3 build muscle in humans?
That has not been demonstrated. There is no published human pharmacokinetic study and no efficacy data for muscle applications. The evidence comes from animal models.
Does follistatin increase muscle mass?
There are no randomised human trials. The striking results come from mice lacking the myostatin gene, whose muscle physiology differs from that of humans.
Why were the ACE-031 trials stopped?
On safety grounds. Some participants developed nosebleeds, bleeding gums and dilated vessels in the skin. The programme was closed in 2013.
Are these peptides allowed in sport?
IGF-1 LR3 is prohibited at all times under category S2 of the World Anti-Doping Agency list. The whole group targets mechanisms covered by anti-doping rules.
Is blocking myostatin safe?
Nothing supports that conclusion in humans. The one programme that reached clinical trials was stopped because of vascular side effects, and no myostatin blocker has been approved for muscle growth since.
Where this information comes from
The structure and mechanism of IGF-1 LR3, the absence of human studies, the risk of hypoglycaemia and of suppressing the body’s own hormonal axis, and its status on the World Anti-Doping Agency list come from material published by Peptpedia on 4 August 2026. The point that neither IGF-1 LR3 nor follistatin has human data for muscle applications comes from a guide published by Know Your Peptide in July 2026. The information on ACE-031, the 2011 halt, the 2013 closure of the programme and the vascular symptoms comes from an article by the Muscular Dystrophy Association dated 2 May 2013. All pages were checked on 31 August 2026.