Editorial note: this article summarises published research on metabolic, fat-loss and mitochondrial peptides. Baclabs does not sell AOD-9604, MOTS-c, SS-31 or any peptide; we supply bacteriostatic water and reconstitution consumables. Nothing here is medical advice.
“Metabolic peptides” is a loose retail category rather than a pharmacological class. It covers a growth hormone fragment that spent six human trials failing to beat placebo for weight loss (AOD-9604, sold interchangeably as HGH Fragment 176-191), a mitochondrial peptide with striking mouse data and one small human trial of an analogue (MOTS-c), a cardiolipin-binding tetrapeptide that is now a licensed medicine in the United States for an ultra-rare disease (SS-31, elamipretide), and a group of small molecules that are not peptides at all but are sold alongside them as “exercise in a pill” (SLU-PP-332, AICAR and 5-Amino-1MQ).
The common thread is that each compound acts on how the body stores, mobilises or burns energy: lipolysis in fat cells, AMP-activated protein kinase (AMPK) signalling in muscle, or the inner mitochondrial membrane itself. What differs enormously is the quality of evidence. This guide sets out what each one is, what the studies actually showed, the doses used, and the UK regulatory position; four supporting articles go deeper.
Most of these compounds arrive as lyophilised powder, so the guide also covers the concentration maths; the reconstitution hub has the full method.
What metabolic peptides are supposed to do
Lipolysis. Fat cells (adipocytes) store triglyceride and release it as free fatty acids when hormone-sensitive lipase is activated, typically through beta-adrenergic receptors. Growth hormone (GH) stimulates this, but it also raises insulin-like growth factor 1 (IGF-1) and blood glucose. The AOD-9604 programme was an attempt to isolate the lipolytic tail of GH from its glucose and growth effects [1].
AMPK activation. AMPK is the cell’s energy sensor. When ATP runs low, AMPK switches on glucose uptake and fatty-acid oxidation and switches off synthesis. Exercise activates it; so do MOTS-c and AICAR in the laboratory [2][3]. Because AMPK activation mimics part of the exercise response, the World Anti-Doping Agency (WADA) lists AMPK activators, naming both AICAR and MOTS-c, as prohibited at all times under section S4.4.1 of the Prohibited List [4].
Mitochondrial membrane stabilisation. SS-31 (elamipretide) binds cardiolipin, a phospholipid in the inner mitochondrial membrane, and is proposed to improve electron transport efficiency and reduce reactive oxygen species [5]. This is about the quality of energy production rather than the signal to burn fuel.
AOD-9604 and HGH Fragment 176-191
These are, for practical purposes, the same molecule. AOD-9604 is a synthetic peptide corresponding to residues 177–191 of human GH with a tyrosine added at the N-terminus for stability, which is why it is also described as fragment 176-191. Metabolic Pharmaceuticals in Melbourne developed it after rodent work from Frank Ng’s group at Monash showed the C-terminal region of GH retained fat-mobilising activity [1][6].
The animal data are consistent. In ob/ob obese mice, 14 days of continuous infusion of either hGH or AOD-9604 reduced weight gain and increased fat oxidation, without the rise in glucose or insulin seen with hGH [1]; a follow-up implicated the beta-3 adrenergic receptor in the chronic effect [7].
The human programme is where the story turns. Between 2001 and 2006, Metabolic Pharmaceuticals ran six randomised, double-blind, placebo-controlled trials in roughly 893 adults, using intravenous doses of 25–400 mcg/kg and oral doses of 0.25–54 mg/day; the largest was a 24-week phase 2b study of oral tablets at 0.25, 0.5 and 1 mg daily in 536 obese adults [8][9]. The 2013 safety paper reports no effect on IGF-1, no antibodies, no serious adverse events and a profile “indistinguishable from placebo” [8]. It does not report weight loss, because there was none worth reporting: the phase 2b study did not separate from placebo and development stopped in 2007. AOD-9604 later gained US “generally recognised as safe” (GRAS) status as a food ingredient [10], a statement about oral safety, not efficacy or injectable use.
Read the HGH Frag 176-191 vs AOD-9604 article for the full trial history, the “no hyperglycaemia” claim examined, and reconstitution tables for 5 mg vials.
MOTS-c and SS-31: the mitochondrial pair
MOTS-c
MOTS-c (mitochondrial open reading frame of the 12S rRNA type-c) is a 16-amino-acid peptide encoded in mitochondrial DNA, identified by Changhan Lee and Pinchas Cohen’s group at USC. In the 2015 Cell Metabolism paper, daily intraperitoneal MOTS-c at 0.5 mg/kg prevented high-fat-diet-induced obesity and insulin resistance in mice and activated AMPK in skeletal muscle, with no effect on weight in mice on a normal diet [2]. A 2021 Nature Communications follow-up showed that exercise raises endogenous MOTS-c in human muscle (11.9-fold) and plasma (1.5-fold), and that 15 mg/kg injections roughly doubled treadmill running time in old mice [11].
The only human interventional data come from CB4211, a modified MOTS-c analogue developed by CohBar. In a 2021 phase 1a/1b study, 20 obese adults with fatty liver received 25 mg subcutaneously daily or placebo for four weeks; liver enzymes and fasting glucose fell significantly, body weight only trended down [12]. The programme has not advanced. Native MOTS-c has no human efficacy trial.
SS-31 (elamipretide)
SS-31 is where the evidence is strongest and the retail story most misleading. Developed by Stealth BioTherapeutics, elamipretide was studied at 40 mg subcutaneously once daily in primary mitochondrial myopathy and Barth syndrome. The phase 3 MMPOWER-3 trial in mitochondrial myopathy failed both primary endpoints: the six-minute walk distance difference versus placebo was −3.2 m [13]. In Barth syndrome, the small TAZPOWER crossover trial also missed its primary endpoints, but the open-label extension showed sustained improvement in knee-extensor strength and walk distance [14].
On that basis, after a complete response letter in May 2025, the FDA granted accelerated approval on 19 September 2025 to Forzinity (elamipretide HCl) to improve muscle strength in Barth syndrome patients weighing at least 30 kg [15]. The label specifies 40 mg subcutaneously once daily from an 80 mg/mL ready-to-use vial, with continued approval contingent on a confirmatory trial [16]. It is not licensed in the UK or EU, and there is no human evidence at all for fat loss or “energy” in healthy adults.
Both compounds are covered in Mitochondrial biogenesis: MOTS-c and SS-31, including dose tables from the literature and reconstitution maths for a 10 mg MOTS-c vial.
Exercise mimetics: SLU-332, AICAR and 5-Amino-1MQ
None of these three is a peptide, but they are sold by the same vendors.
SLU-PP-332 (usually shortened to SLU-332 in listings) is a synthetic agonist of the oestrogen-related receptors ERRα, β and γ, developed in Thomas Burris’s laboratory. In mice, 50 mg/kg intraperitoneally twice daily for 7–15 days increased oxidative type IIa muscle fibres and let mice run about 70 per cent longer; the effect disappeared in muscle-specific ERRα knockouts [17]. A second paper in diet-induced obese mice reported roughly 12 per cent lower body weight after 28 days on the same regimen, with reduced fat mass and improved glucose tolerance [18]. There are no human data of any kind.
AICAR (5-aminoimidazole-4-carboxamide ribonucleoside, clinical name acadesine) is an AMP analogue that activates AMPK. Narkar and colleagues showed in 2008 that four weeks of AICAR at 500 mg/kg/day improved running endurance in untrained mice by around 44 per cent, the origin of “exercise in a pill” [3]. As acadesine it was trialled intravenously for cardioprotection; the RED-CABG trial was stopped for futility in 2012 [19]. WADA prohibits it at all times [4].
5-Amino-1MQ (5-amino-1-methylquinolinium) inhibits nicotinamide N-methyltransferase (NNMT), raising intracellular NAD+ and suppressing lipogenesis. In diet-induced obese mice, 20 mg/kg subcutaneously three times daily for 11 days produced about 5 per cent weight loss and a 35 per cent fall in epididymal fat mass without reducing food intake [20]; a 2024 follow-up added oral pharmacokinetics and fatty-liver outcomes [21]. No human trial exists.
The exercise-mimetic compounds article compares the three mechanisms and explains why “exercise in a pill” is a mouse result, not a human one.
Lipotropic injections: L-carnitine, Lipo-B, Lipo-C and Lemon Bottle
At the other end of the market are clinic-administered “fat-burning” injections. L-carnitine is the only ingredient with reasonable human data: a 2020 meta-analysis of 37 randomised trials found oral supplementation reduced body weight by a mean of 1.21 kg and fat mass by 2.08 kg, plateauing at 2,000 mg/day [22]. That is a modest oral effect, not evidence for injections.
Lipo-B and Lipo-C are compounded mixtures of methionine, inositol and choline (MIC) with vitamin B12. The lipotrope concept comes from 1950s rat liver studies; no controlled trial shows MIC injections cause weight loss in humans. In the UK every injectable medicine is prescription-only by law, and the government confirmed in April 2025 that the MHRA cannot reclassify B12 injections [23].
Lemon Bottle is a Korean “lipolysis solution” (declared ingredients bromelain, riboflavin and lecithin) sold as a cosmetic. It is not a licensed medicine anywhere. The MHRA has said that, absent medicinal claims or an active pharmaceutical ingredient, it falls outside medicines regulation; Swissmedic testing in 2024 found batches containing only caffeine, or none of the declared ingredients; and the General Pharmaceutical Council warned UK pharmacies in April 2025 that such products “have potentially caused serious harm” [24][25][26]. The lipotropic injections article sets all of this out in detail.
Doses reported in the literature
The doses below are those used in the cited studies, not recommendations; most are rodent figures that cannot be scaled to humans by body weight alone.
| Compound | Model | Dose in source | Route | Source |
|---|---|---|---|---|
| AOD-9604 | Obese mice | Continuous infusion, 14 days | Osmotic pump | [1] |
| AOD-9604 | 893 adults, six trials | 25–400 mcg/kg IV; 0.25–54 mg/day oral | IV / oral | [8] |
| MOTS-c | Mice, high-fat diet | 0.5 mg/kg/day, 8 weeks | Intraperitoneal | [2] |
| MOTS-c | Old mice | 15 mg/kg, 3x weekly | Intraperitoneal | [11] |
| CB4211 (MOTS-c analogue) | 20 obese adults | 25 mg daily, 4 weeks | Subcutaneous | [12] |
| Elamipretide (SS-31) | Barth syndrome, licensed (US) | 40 mg once daily | Subcutaneous | [16] |
| SLU-PP-332 | Mice | 50 mg/kg twice daily | Intraperitoneal | [17][18] |
| AICAR | Mice | 500 mg/kg/day, 4 weeks | Intraperitoneal | [3] |
| 5-Amino-1MQ | Obese mice | 20 mg/kg three times daily, 11 days | Subcutaneous | [20] |
| L-carnitine | Meta-analysis, 2,292 adults | Up to 2,000 mg/day | Oral | [22] |
Reconstitution: the maths for lyophilised metabolic peptides
AOD-9604, MOTS-c and research-grade SS-31 are supplied as freeze-dried powder. (Licensed elamipretide is a ready-to-use solution.) The formula is:
Concentration (mg/mL) = vial content (mg) ÷ diluent volume (mL), and on a U-100 insulin syringe (100 units = 1 mL) each unit = concentration (mg/mL) × 10 mcg.
Worked example: a 5 mg AOD-9604 vial plus 2 mL bacteriostatic water gives 2.5 mg/mL, which is 2,500 mcg/mL, so each unit on a U-100 syringe holds 25 mcg. A 10 mg MOTS-c vial plus 2 mL gives 5 mg/mL, or 50 mcg per unit.
| Vial | Diluent added | Concentration | mcg per U-100 unit | Units for 1 mg |
|---|---|---|---|---|
| AOD-9604 5 mg | 1 mL | 5 mg/mL | 50 mcg | 20 |
| AOD-9604 5 mg | 2 mL | 2.5 mg/mL | 25 mcg | 40 |
| MOTS-c 10 mg | 1 mL | 10 mg/mL | 100 mcg | 10 |
| MOTS-c 10 mg | 2 mL | 5 mg/mL | 50 mcg | 20 |
| SS-31 10 mg | 1 mL | 10 mg/mL | 100 mcg | 10 |
| SS-31 50 mg | 2 mL | 25 mg/mL | 250 mcg | 4 |
A multi-dose vial is punctured repeatedly, so it needs a preserved diluent. Bacteriostatic water contains 0.9 per cent benzyl alcohol, suitable for multi-dose use for up to 28 days after first puncture; sterile water has no preservative. The distinction is explained in bacteriostatic water vs sterile water, and the storage rules in bacteriostatic water storage and shelf life. Baclabs supplies UK-stocked bacteriostatic water in 30 mL vials; the reconstitution guide has step-by-step method and further tables.
UK legal and safety position
None of the peptides in this guide is licensed as a medicine in the UK. Elamipretide has a US licence for one ultra-rare disease; AOD-9604’s GRAS status covers oral food use in the US. Everything else is sold under “research use only” labelling because supplying an unlicensed product for human use would engage the Human Medicines Regulations 2012. B12, L-carnitine and MIC injections are prescription-only because all injectables are.
On safety, the honest position is asymmetric. AOD-9604 has around 900 trial participants showing a placebo-like adverse-event profile [8]. Elamipretide’s licensed label lists injection-site reactions and transient eosinophilia [16]. MOTS-c, SLU-PP-332 and 5-Amino-1MQ have no human safety data; the FDA has flagged MOTS-c and AOD-9604 for immunogenicity concerns and limited safety information in its compounding reviews [27]. Athletes should note that AICAR and MOTS-c are named WADA-prohibited substances [4].
Frequently asked questions
Which metabolic peptide has the best evidence for fat loss?
None has good human evidence. AOD-9604 is the only one with large placebo-controlled trials, and it did not beat placebo for weight loss. MOTS-c and SLU-PP-332 have rodent data only. If the goal is weight loss with evidence behind it, the licensed GLP-1 medicines covered in the GLP-1 peptides guide are in a different category entirely.
Is AOD-9604 the same as HGH Fragment 176-191?
Essentially yes. AOD-9604 is hGH residues 177–191 with an added N-terminal tyrosine, which is why vendors call it fragment 176-191. Both names describe the same 16-amino-acid sequence. The differences between products on the market are about purity and supplier, not molecule.
Is SS-31 approved for anything?
Yes. Elamipretide (Forzinity) received US FDA accelerated approval in September 2025 to improve muscle strength in Barth syndrome patients weighing at least 30 kg, at 40 mg subcutaneously daily. It is not approved for any other condition, is not licensed in the UK or EU, and has no human data for fat loss.
Are MOTS-c and AICAR banned in sport?
Yes. Both are named as AMPK activators under section S4.4.1 of the WADA Prohibited List and are banned at all times, in and out of competition. SLU-PP-332 is not named but ERR agonists sit within the same “metabolic modulators” logic, and athletes should treat it as high-risk.
References
- Increase of fat oxidation and weight loss in obese mice caused by chronic treatment with human growth hormone or a modified C-terminal fragment. Heffernan et al., International Journal of Obesity, 2001
- The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance. Lee et al., Cell Metabolism, 2015
- AMPK and PPARδ agonists are exercise mimetics. Narkar et al., Cell, 2008
- The Prohibited List, section S4.4.1 (AMPK activators). World Anti-Doping Agency, 2026
- Elamipretide: a review of its structure, mechanism of action, and therapeutic potential. Tung et al., International Journal of Molecular Sciences, 2025
- Molecular and cellular actions of a structural domain of human growth hormone (AOD9401) on lipid metabolism in Zucker fatty rats. Ng et al., Journal of Molecular Endocrinology, 2000
- The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and β3-AR knock-out mice. Heffernan et al., Endocrinology, 2001
- Safety and tolerability of the hexadecapeptide AOD9604 in humans. Stier, Vos and Kenley, Journal of Endocrinology and Metabolism, 2013
- Metabolic Pharmaceuticals’ obesity trial update: first 100 subjects complete the phase 2B trial of AOD9604. BioSpace press release, 2006
- Safety and metabolism of AOD9604, a novel nutraceutical ingredient for improved metabolic health. Moré and Kenley, Journal of Endocrinology and Metabolism, 2014
- MOTS-c is an exercise-induced mitochondrial-encoded regulator of age-dependent physical decline and muscle homeostasis. Reynolds et al., Nature Communications, 2021
- CohBar announces positive topline results from the phase 1a/1b study of CB4211. GlobeNewswire, 2021
- Efficacy and safety of elamipretide in individuals with primary mitochondrial myopathy: the MMPOWER-3 randomized clinical trial. Karaa et al., Neurology, 2023
- A phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the effectiveness of elamipretide in Barth syndrome. Thompson et al., Genetics in Medicine, 2021
- Stealth BioTherapeutics announces FDA accelerated approval of Forzinity (elamipretide HCl). PR Newswire, 2025
- Forzinity (elamipretide hydrochloride) injection: prescribing information. DailyMed, US National Library of Medicine, 2025
- Synthetic ERRα/β/γ agonist induces an ERRα-dependent acute aerobic exercise response and enhances exercise capacity. Billon et al., ACS Chemical Biology, 2023
- A synthetic ERR agonist alleviates metabolic syndrome. Billon et al., Journal of Pharmacology and Experimental Therapeutics, 2024
- Effect of adenosine-regulating agent acadesine on morbidity and mortality associated with coronary artery bypass grafting: the RED-CABG randomized controlled trial. Newman et al., JAMA, 2012
- Selective and membrane-permeable small molecule inhibitors of nicotinamide N-methyltransferase reverse high fat diet-induced obesity in mice. Neelakantan et al., Biochemical Pharmacology, 2018
- Nicotinamide N-methyltransferase inhibition mitigates obesity-related metabolic dysfunction. Babula et al., Diabetes, Obesity and Metabolism, 2024
- Effects of L-carnitine supplementation on weight loss and body composition: a systematic review and meta-analysis of 37 randomized controlled clinical trials. Talenezhad et al., Clinical Nutrition ESPEN, 2020
- Written question 44657: Vitamin B12 injections, prescription-only status. UK Parliament, Department of Health and Social Care, 2025
- Navigating hype products (MHRA position on Lemon Bottle). IMCAS, 2024
- Swissmedic issues warning about the illegal medicinal product “Lemon Bottle” lipolysis solution. Swissmedic, 2024
- GPhC issues warning on sales of “fat-dissolving” Lemon Bottle injections. Pharmacy Magazine, 2025
- Certain bulk drug substances for use in compounding that may present significant safety risks. US Food and Drug Administration, 2025
Disclaimer: This content is for educational purposes only and does not constitute medical advice. Bacteriostatic water is supplied for reconstitution of substances intended for research and for use as directed by a healthcare professional. Peptides and medicines discussed here may be unlicensed in the UK or prescription-only; consult a qualified clinician before using any medicine. Baclabs does not sell peptides.