SLU-PP-332

SLU-PP-332 is a synthetic small molecule designed to activate the estrogen-related receptors (ERRα, ERRβ and ERRγ), a family of nuclear receptors that control mitochondrial and oxidative metabolism. It was developed in the laboratory of Thomas Burris at Saint Louis University, which is where the SLU in its code name comes from. It acts as a pan-agonist, meaning it engages all three receptors, with the greatest potency at ERRα.

The first point to settle is a labeling problem that follows this compound everywhere. SLU-PP-332 is not a peptide. Peptides are short chains of amino acids joined by peptide bonds, conventionally 2 to 50 residues long. SLU-PP-332 has a molecular formula of C₁₈H₁₄N₂O₂ and a molecular weight of roughly 290 g/mol, which is about one fifth the size of a small research peptide such as BPC-157. It contains no amino acids and no peptide bonds, and it therefore has no sequence to report. It is a nuclear receptor ligand, in the same broad pharmacological family as compounds like GW501516 or SR9009, not in the family of injectable research peptides.

This distinction is not pedantic. It changes almost everything about how the molecule behaves. Peptides are usually degraded in the gut and act on receptors at the cell surface. A small-molecule nuclear receptor agonist like SLU-PP-332 is absorbed and distributed differently, crosses cell membranes, and works inside the nucleus by changing which genes are transcribed. It also means that none of the general assumptions people carry over from peptide research, including assumptions about tolerability, clearance or detection, apply here.

The reason the confusion persists is commercial. Vendors that sell research peptides have added SLU-PP-332 to the same catalogs and the same marketing language, so it is routinely described as the "exercise peptide". If you see that phrasing, treat it as a signal that the source is not being careful with basic pharmacology. For context on how genuine peptides are classified and studied, our overview of peptide safety and evidence standards is a useful starting point.

An exercise mimetic is a compound that reproduces part of the molecular signature of physical exercise without the physical exercise. The term entered mainstream pharmacology in 2008, when Narkar and colleagues reported in Cell that activators of AMP-activated protein kinase (AMPK) and agonists of the nuclear receptor PPARδ could induce exercise-associated gene programs in mouse skeletal muscle. In that study, four weeks of AICAR treatment alone induced metabolic genes and increased running endurance in sedentary mice by 44 percent.

It is important to read the word "mimetic" narrowly. What these compounds mimic is a transcriptional response: the switching on of genes involved in mitochondrial biogenesis, fatty acid oxidation and oxidative fiber specification. Exercise does far more than that. It loads bone and tendon, improves vascular function and blood pressure, modifies appetite and sleep, changes insulin signaling across multiple tissues, affects mood and cognition, and produces coordinated adaptations in the heart, lungs and nervous system. No current molecule reproduces that package, and none has been shown to deliver the long-term health outcomes that exercise delivers in humans.

The legitimate scientific motivation behind this field is clinical, not athletic. A substantial number of patients cannot exercise meaningfully: people with advanced heart failure, severe obesity with mobility limitation, neuromuscular disease, cachexia, or prolonged immobilization. A pharmacological way to maintain oxidative muscle metabolism in those populations would be genuinely valuable, which is why academic groups keep working on it.

The athletic and body composition interest that has grown around these compounds runs well ahead of the data. Rodent endurance gains on a treadmill are a signal that a pathway is engaged. They are not evidence that a trained human will run faster, recover better, or lose fat safely. Readers comparing options in this space should also see our broader discussion of what the literature supports for peptides studied in athletic contexts, where the same evidence gap recurs repeatedly.

The estrogen-related receptors are often described as orphan nuclear receptors: despite the name, they are not activated by estrogen and no endogenous ligand has been firmly established for them. They are constitutively active transcription factors, and their activity is governed largely by how much coactivator protein, particularly PGC-1α, is available to them. PGC-1α is itself strongly induced by exercise, which is the mechanistic bridge that makes ERR an attractive target for an exercise mimetic.

Together, ERR and PGC-1α act as a master control module for oxidative metabolism. They regulate genes for mitochondrial biogenesis, the electron transport chain, the tricarboxylic acid cycle, fatty acid uptake and beta-oxidation, and the specification of oxidative muscle fiber types. SLU-PP-332 was designed to increase ERR transcriptional output, which in the published cell work translated into increased mitochondrial function and cellular respiration in a skeletal muscle cell line.

In mice, that molecular effect produced a measurable shift in muscle phenotype. Billon and colleagues reported an increase in type IIa oxidative skeletal muscle fibers and the induction of an acute aerobic exercise gene program in skeletal muscle. Critically, the effect was receptor-dependent: in animals lacking ERRα, the endurance benefit was lost, which is strong internal evidence that the compound works through the intended target rather than through an off-target mechanism.

One consequence of this mechanism deserves attention. ERRs are not confined to skeletal muscle. They are highly expressed in the heart, kidney, brown adipose tissue and other metabolically active organs, and ERR signaling is studied in oncology because tumor cells also depend on oxidative and biosynthetic metabolism. A systemically administered pan-agonist therefore does not act on muscle alone. That is precisely why the heart data described below exist, and also why chronic systemic ERR activation in humans cannot be assumed to be benign on the basis of a few weeks of mouse dosing.

The published record for SLU-PP-332 is entirely preclinical, and it rests on three primary papers plus one medicinal chemistry follow-up.

Exercise capacity (ACS Chemical Biology, 2023). Billon and colleagues characterized SLU-PP-332 as a pan-ERR agonist with the highest potency at ERRα, showed increased mitochondrial function and respiration in a skeletal muscle cell line, and tested it in sedentary mice. Treated animals were reported to run roughly 70 percent longer and about 45 percent farther before exhaustion than vehicle-treated animals, alongside an increase in type IIa oxidative fibers. The benefit required ERRα, as it was absent in ERRα knockout mice.

Metabolic syndrome and fat mass (Journal of Pharmacology and Experimental Therapeutics, 2024). The same group studied diet-induced obese mice and genetically obese ob/ob mice, with 8 to 10 male animals per group, administering 50 mg/kg by intraperitoneal injection twice daily for 28 days in the diet-induced model and 12 days in the ob/ob model. Treatment increased whole-body energy expenditure and fatty acid oxidation, reduced fat mass accumulation, lowered cholesterol and triglycerides, and improved insulin sensitivity, without a change in food intake. Those mouse milligram-per-kilogram figures are reported here only as study parameters. They cannot be converted into a human dose, and no human-equivalent dose has been established for this compound.

Cardiac function (Circulation, 2024). Xu and colleagues tested SLU-PP-332 and a structurally distinct analogue, SLU-PP-915, in a mouse model of pressure overload induced heart failure. Both compounds improved ejection fraction, reduced fibrosis and increased survival without affecting cardiac hypertrophy, with effects attributed largely to ERRγ and to a broad transcriptional activation of fatty acid metabolism and mitochondrial genes.

Chemistry follow-up (International Journal of Biological Macromolecules, 2026). A structure-activity relationship study of the SLU-PP-332 scaffold reported that the original compound remains a benchmark for ERR activation, while several analogues achieved comparable transcriptional responses with improved ligand efficiency, solubility or metabolic stability. In plain terms, the medicinal chemistry has moved on, which is itself a comment on SLU-PP-332's drug-like limitations.

The limitations of this body of work are structural rather than incidental. Every efficacy finding comes from rodents, largely male rodents, over days to weeks, using injected administration. There are no published long-term toxicology, carcinogenicity, reproductive or cardiac safety studies at chronic exposure, and no data in trained animals or in females at comparable depth. Metabolic and endurance results in mice have an unimpressive historical track record of translating to human outcomes, as readers familiar with the evidence behind fat loss compounds will recognize.

SLU-PP-332 is usually discussed alongside two other molecules labeled exercise mimetics. They work through different targets and sit at different points on the evidence curve, but they share the same central limitation: none has been shown in humans to substitute for training.

MOTS-c. Unlike SLU-PP-332, MOTS-c genuinely is a peptide: a 16 amino acid molecule encoded within mitochondrial DNA. Lee and colleagues reported in 2015 that it regulates insulin sensitivity and metabolic homeostasis through AMPK and that it reduced diet-induced obesity and insulin resistance in mice. Reynolds and colleagues later characterized it as an exercise-induced mitochondrial-encoded regulator of age-dependent physical decline and muscle homeostasis, with circulating levels responsive to exercise. Human evidence remains thin: a modified analogue reached an early-phase company-sponsored trial, and development did not continue, so there is no robust efficacy dataset in people. Our dedicated MOTS-c guide covers that literature in detail, and the comparison between blended peptides and MOTS-c addresses how it is positioned commercially.

AICAR. AICAR is the compound that launched the exercise mimetic concept in 2008 and is also the cautionary tale of the field. Under the name acadesine it was taken into large human trials for a different indication. The RED-CABG trial published in JAMA in 2012 randomized 3,080 intermediate to high risk patients undergoing coronary artery bypass grafting and was stopped early at a prespecified futility analysis, having failed to show a reduction in morbidity or mortality versus placebo. Acadesine was never approved for any indication. A compound can activate the right pathway, pass through extensive human testing, and still deliver nothing clinically useful.

Read in sequence, these three molecules describe a gradient of uncertainty. AICAR has human exposure data and a negative pivotal trial. MOTS-c has strong rodent biology and a single truncated early clinical program. SLU-PP-332 has the most striking rodent results and the least human information of the three, which is exactly the combination that tends to generate enthusiasm online.

The honest answer is that nothing is known. There is no published clinical trial of SLU-PP-332, no published human pharmacokinetic or tolerability dataset, and no registered trial that we were able to identify. The absence of reported adverse effects in humans is not a safety finding. It is the predictable consequence of a compound that has never been formally studied in people.

What has been published in 2026 is analytical rather than clinical. Two independent laboratory groups, one at the UCLA Olympic Analytical Laboratory and one in the German anti-doping research community, characterized the Phase I and Phase II metabolites of SLU-PP-332 using in vitro systems such as pooled human liver preparations, identifying hydroxylated, reduced, glucuronidated and sulfated metabolites. These are detection studies, designed so that doping control laboratories can find the compound. They tell us something about how human enzymes would process the molecule, and nothing about whether those metabolites are safe, what blood levels any given intake would produce, or what happens after weeks of exposure.

Several mechanistic concerns follow directly from the pharmacology and remain unresolved. ERR receptors are broadly expressed in the heart, kidney and other tissues, so a systemic pan-agonist acts far beyond skeletal muscle. ERR signaling intersects with tumor metabolism, which is a question any chronic ERR-activating agent must eventually answer in formal toxicology. The medicinal chemistry literature itself notes that the original scaffold has suboptimal drug-like properties, which is why analogues were developed. None of these issues can be settled by rodent studies lasting a few weeks.

There is also a product quality dimension that is independent of the pharmacology. Material sold online as SLU-PP-332 is not manufactured to pharmaceutical standards, is not subject to pharmacopeial identity, purity or endotoxin testing, and is frequently mislabeled as a peptide by the vendors themselves. Identity and purity of grey-market material are unverifiable by the end user.

Medical disclaimer: this article is for educational purposes only and is not medical advice. SLU-PP-332 is not approved by the FDA, the EMA or any other regulator for human use, and its legal status varies by jurisdiction. Consult a qualified healthcare professional before considering any investigational compound. We do not provide dosing information or administration protocols for this molecule, because no evidence base exists from which to derive them.

For any athlete subject to anti-doping rules, the practical answer is yes. The World Anti-Doping Agency Prohibited List opens with section S0, Non-Approved Substances, which prohibits at all times any pharmacological substance that is not addressed by another section of the List and that has no current approval by any governmental regulatory health authority for human therapeutic use, explicitly including drugs under preclinical or clinical development. SLU-PP-332 is a textbook example of an S0 substance.

The List's metabolic modulator section is also relevant context. In the 2026 edition, section S4.5 names specific examples of prohibited metabolic modulators, including AMPK activators such as BAM15, AICAR and MOTS-c, the PPARδ agonist GW1516 (also known as GW501516), and the Rev-erbα agonists SR9009 and SR9011. In the text we reviewed, ERR agonists are not listed as a named example and SLU-PP-332 does not appear by name. That is not a loophole. The List's examples are illustrative rather than exhaustive, and S0 already captures non-approved investigational compounds regardless of mechanism.

Detection is moving quickly. The two 2026 metabolite papers exist specifically because doping control laboratories anticipate misuse and need to know which analytical targets to monitor by liquid chromatography and high-resolution mass spectrometry. Athletes should assume that the gap between a compound circulating in grey markets and a validated assay in accredited laboratories is narrowing, and that retrospective analysis of stored samples is a routine possibility.

A further point is often missed. A Therapeutic Use Exemption requires a legitimate medical indication and an approved treatment. A compound with no regulatory approval anywhere cannot support a TUE. For athletes weighing compounds marketed for endurance or recovery, our review of what the evidence supports in athletic populations sets out the same risk calculus across this category.

SLU-PP-332 occupies a familiar commercial space. It was published in high-profile journals, it has a memorable story attached to it (the drug that makes mice run farther and lose fat), and it has no approved status that would restrict its sale as a laboratory reagent. Legitimate chemical suppliers list it as a research tool compound for in vitro and animal work, which is appropriate. A second tier of vendors then resells it alongside research peptides with consumer-style marketing, dosing charts and reconstitution instructions.

Those consumer-facing dosing charts have no scientific basis. There is no published human pharmacokinetic study to anchor a dose, no tolerability study to define an upper limit, and no clinical endpoint against which any regimen could be judged effective. Figures circulating online are typically derived by allometric scaling from mouse experiments, which is a hypothesis-generating exercise used in early drug development, not a method for determining what a person should take. Scaling also silently assumes that the human safety profile resembles the mouse profile, which is the precise assumption that formal Phase 1 trials exist to test.

The regulatory position is straightforward. SLU-PP-332 has not been approved by the FDA, the EMA or any comparable authority for human use. Selling it for human consumption, or marketing it with human health claims, is not permitted in most jurisdictions, and products sold for research use are exempt from the manufacturing and labeling controls that apply to medicines. Import rules and possession rules vary by country, and buyers carry that legal exposure themselves.

One final signal is worth watching. The academic group that created SLU-PP-332 has already published analogues with better solubility and metabolic stability, and the cardiac work was conducted with both SLU-PP-332 and SLU-PP-915. When a laboratory moves beyond its own lead compound, that is usually a statement about the lead compound's drug-like shortcomings rather than an endorsement of it.

The list of open questions is longer than the list of established facts, and it is worth stating plainly.

• Human pharmacokinetics. Absorption, bioavailability, half-life, distribution and clearance in humans are unpublished. Metabolite identification has been done only in in vitro systems.
• Any safe human exposure range. No dose-finding study exists, so there is no established no-effect level, no therapeutic window and no maximum tolerated exposure.
• Chronic safety. There are no published long-term toxicology, cardiac, hepatic, renal, reproductive or carcinogenicity studies at sustained exposure. Given that ERR signaling is implicated in tumor metabolism and is active in the heart and kidney, these are not optional questions.
• Whether the gene signature translates. Inducing an aerobic gene program is a mechanism, not an outcome. Whether that produces measurable changes in VO₂ max, time to exhaustion, body composition or metabolic health in humans is untested.
• Sex differences. The pivotal metabolic work used male mice. ERR biology interacts with the broader nuclear receptor landscape, and female data at comparable depth are lacking.
• Interaction with actual training. Whether ERR agonism adds to, duplicates or interferes with adaptations from real exercise is unknown. In the earlier AICAR and PPARδ literature, drug and training effects were partly overlapping rather than simply additive.
• Comparative value. No study has compared SLU-PP-332 with structured exercise, and none has compared it head to head with MOTS-c, AICAR or any approved metabolic agent in the same model.
• Development path. Whether SLU-PP-332 itself, or a successor such as SLU-PP-915 or one of the newer analogues, ever enters formal human testing remains to be seen.

The way this uncertainty gets resolved is conventional and slow: formal toxicology, an investigational new drug application, a Phase 1 safety and pharmacokinetic study in healthy volunteers, then controlled efficacy trials with hard endpoints in a defined patient population. Until at least the first of those steps is publicly completed, any claim about what SLU-PP-332 does in a human body is extrapolation from mice.

That is not a verdict against the science. The ERR and PGC-1α axis is a well-reasoned target, the rodent data are internally consistent, and the receptor-dependence experiments are the kind of rigor that strengthens a mechanistic claim. It is a verdict about the gap between an interesting preclinical compound and something a person can reasonably use. Readers interested in how that gap is evaluated across this field more generally can continue with our article on how to assess safety claims in peptide and research compound markets.