S23: A Literature Course — What the Published Record Covers and Where It Stops

How to use this course. Each module below asks one question that a reader would need answered before treating any statement about S23 as evidence-based, explains what kind of published work could answer it, and then states plainly what the verified citation set behind this page does and does not contain. This page is for educational purposes only and is not medical advice; consult a licensed physician for any question about a medicine, a supplement or a research chemical. Nothing here is an instruction, a protocol or an endorsement, and no dose is given.

The single most important point: the verified evidence set assembled for this page contains no primary studies of S23. That is not a rhetorical framing — it is the reason this course reports no doses, no efficacy outcomes and no adverse-event frequencies for S23. Where papers are cited below, they are cited as examples of study design and endpoint measurement in unrelated research areas, and every such sentence says so.

Module 1 — What S23 Is and How Compounds Like It Are Studied

Definition and class

S23 is commonly catalogued as a non-steroidal small molecule of the selective androgen receptor modulator (SARM) class. Two points of basic taxonomy matter for readers arriving from the phrase "S23 peptide":

• It is not a peptide. Peptides are short chains of amino acids joined by amide bonds. SARMs are synthetic non-steroidal organic molecules, and the SARM label refers to a proposed receptor-selectivity profile rather than to a chemical family.
• It has no international non-proprietary name and no brand name, because it is not a marketed medicine. The alphanumeric code is a development-style designation, which is why it appears in chemical catalogues rather than in drug formularies.

Forms encountered

Material labelled S23 is typically offered as a powder or as a solution in a carrier such as ethanol or propylene glycol, with labelling that restricts it to laboratory use. Because there is no pharmacopoeial monograph, there is no reference standard for identity, purity or content that a purchaser or a reader could compare a certificate of analysis against.

What a proper identity paper looks like

Readers can calibrate expectations by looking at what chemical characterisation papers actually contain. In a 2024 report, researchers described the isolation and structural characterisation of a new flavan-3-ol from Sargentodoxae Caulis, documenting the compound as a defined chemical entity rather than as a trade name (PMID 39701731). Similarly, a 2021 synthetic chemistry study reported molecular cages self-assembled by imine condensation in water, with the structural claims tied to the reaction chemistry that produced them (PMID 33252164). Those are the kinds of primary records — structure, synthesis, analytical confirmation — that anchor a compound in the literature.

Limits of the evidence (Module 1)

No paper in the verified set characterises S23, establishes its purity profile, or describes its synthesis. Descriptions of S23 in circulation therefore rest on vendor documentation, chemical databases and secondary commentary, none of which were peer-reviewed primary sources for this page. Class membership ("a SARM") is a label, not a finding.

Module 2 — Mechanism as Described in the Literature

What a mechanism claim requires

A mechanistic claim for any androgen-receptor-directed molecule would normally be supported by a chain of published work: receptor binding affinity measurements, reporter-gene or transactivation assays, tissue-selectivity comparisons across androgen-responsive tissues, and in vivo confirmation that the molecular event tracks with an organ-level change. Each link in that chain is a separate publication with its own methods and controls.

Molecular-target research of that shape can be seen in a 2026 oncology study, in which researchers reported that co-targeting MRPS7-23 synergistically enhanced cisplatin efficacy and suppressed nasopharyngeal carcinoma growth and metastasis in the models the study used (PMID 41522354). The structure of that paper — a named molecular target, a defined intervention, a growth and metastasis endpoint — is the structure a mechanism-to-outcome argument needs. A second example of mechanism-level work is a 2022 study in which researchers reported that miR-98-5p suppressed liver fibrosis by targeting TGFβ receptor 1, linking a specific molecular interaction to a measured tissue outcome (PMID 35188624).

Limits of the evidence (Module 2)

The verified set contains no binding-affinity data, no transactivation assay data and no tissue-selectivity data for S23. Statements that appear online describing how S23 "works" — including claims about androgen receptor selectivity, suppression of endogenous hormone production, or effects on particular tissues — are not reproduced here, because no citation in this page's evidence set supports them. A plausible mechanism is a hypothesis until a study measures it.

Module 3 — Reported Outcomes by Study

What this module would contain if the data existed

A normal outcomes module is a table: one row per study, with columns for model (cell line, rodent strain, human participants), the intervention and its duration, the pre-specified endpoint, and the direction and size of the result. The table below shows the column headings that a reader should look for — and what the verified set returns for S23.

By contrast, well-specified outcome reporting is visible in unrelated fields. In a 2023 diagnostic study, researchers assessed hepatic steatosis using ultrasound attenuation imaging with liver biopsy correlation, so that an imaging readout was benchmarked against a reference standard (PMID 35466506). In a 2022 study, magnetic resonance imaging was reported to improve stratification of fibrosis and steatosis in patients with chronic liver disease (PMID 35962809). In a 2026 multicenter study, a sequential combination of the Fibrosis-4 index and Mac-2 binding protein glycosylation isomer improved detection of advanced fibrosis in metabolic dysfunction-associated steatotic liver disease (PMID 42006192). Each of those studies names the population, the measurement and the comparison — which is exactly what is absent for S23.

Limits of the evidence (Module 3)

Because there are no S23 outcome studies in the verified set, there is no basis on this page for any statement about benefits, performance, body composition, strength or any other endpoint. Anecdotal reports, forum summaries and marketing copy are not study data, and they carry no denominator, no control group and no blinding.

Module 4 — S23 Side Effects: What Studies Report

The honest answer

The verified citation set for this page reports no adverse events for S23, because it contains no S23 studies. Absence of published harm data is not the same as evidence of safety; it means the safety question has not been answered in the sources available here. Unapproved compounds distributed for laboratory use have no pharmacovigilance system behind them — no mandated reporting, no periodic safety update reports and no label warnings derived from trial data.

How safety endpoints are actually measured

Readers evaluating any future S23 safety claim can ask whether the endpoint was measured with a validated method. For liver endpoints, researchers have used biopsy-correlated ultrasound attenuation imaging to assess hepatic steatosis (PMID 35466506), MRI to stratify fibrosis and steatosis in chronic liver disease (PMID 35962809), and sequential blood-based indices combining FIB-4 with M2BPGi to detect advanced fibrosis (PMID 42006192). For haematologic and renal questions, a 2026 physiology study examined the cellular microenvironment of erythropoietin-producing cells in hypoxic and injured mouse kidneys, illustrating how erythropoietin biology is interrogated at tissue level (PMID 41504852). A safety claim that rests on self-report rather than on measurements of this kind is a weaker claim, whatever direction it points in.

Limits of the evidence (Module 4)

The papers cited immediately above are methodological examples from unrelated fields; none of them studied S23, and none of them reported an adverse event attributable to S23 or to any SARM. No frequency, severity grade, reversibility or monitoring interval for S23 can be inferred from this page.

Module 5 — Pharmacokinetics Where Data Exist

The parameters that would be needed

A pharmacokinetic profile is a specific list: oral bioavailability, time to maximum concentration, maximum concentration, area under the curve, volume of distribution, clearance route, metabolising enzymes, half-life and accumulation on repeated administration. Half-life in particular is the parameter most often quoted for research chemicals and least often traceable to a published human study.

What the verified set contains

No paper in the verified set reports any pharmacokinetic parameter for S23 in any species. For that reason this course states no half-life, no bioavailability figure and no clearance pathway. Readers encountering a numeric half-life for S23 can reasonably ask which species it was measured in, by which assay, in how many subjects, and in which publication — and treat an unsourced number as unsourced.

Limits of the evidence (Module 5)

Without pharmacokinetic data there is no way to reason about exposure, and without exposure data there is no way to interpret either an effect or an adverse event, even if one were reported. This module is therefore empty by necessity rather than by editorial choice.

Module 6 — Regulatory Status, Stated Factually

Approved products

There is no S23-containing medicine approved by the U.S. Food and Drug Administration, the European Medicines Agency or comparable regulators. No SARM has completed the approval pathway for marketing as a drug in the United States. Consequently S23 has no approved indication, no approved labelling and no approved strength or route of administration.

Research-use-only status

Material sold as S23 is generally labelled "for research use only — not for human consumption." That phrase is a distribution status, not a safety assessment: it signals that the material has not been manufactured, tested or labelled to pharmaceutical standards. It also means identity and purity rest on the seller's own documentation.

Compounding

In the United States, pharmacy compounding under sections 503A and 503B of the Federal Food, Drug, and Cosmetic Act requires a bulk drug substance that is a component of an FDA-approved drug, appears in an applicable United States Pharmacopeia monograph, or is included on the relevant FDA bulks list. A substance meeting none of those conditions is not an eligible compounding ingredient, and S23 is not a component of an approved product.

Sport and supplement context

SARMs are included in the anabolic agents section of the World Anti-Doping Agency Prohibited List, which applies in and out of competition for athletes under the World Anti-Doping Code. Separately, SARMs are not lawful dietary ingredients in the United States, and the FDA has publicly warned about products marketed as containing them. Regulatory status can differ by country and can change; this section is factual background and not legal advice.

Limits of the evidence (Module 6)

Regulatory status describes how a substance is treated administratively. It does not quantify risk, and it does not substitute for the missing clinical data described in Modules 3 to 5.

What the Studies Did Not Test

Even a generous reading of the available record leaves the following untested for S23 in the verified evidence set:

1. Any human endpoint. No trial in this set enrolled participants, so nothing is known here about efficacy, tolerability or dose-response in people.
2. Long-term exposure. No study in this set followed any subject beyond a single exposure window, so persistence and reversibility of any change are unaddressed.
3. Special populations. No data in this set address adolescents, older adults, pregnancy or lactation, or people with hepatic, renal, cardiac or endocrine disease.
4. Interactions. No study in this set examined co-administration with prescription medicines, hormones or other research chemicals.
5. Product quality. No study in this set analysed retail material labelled S23 for identity, content or contamination.
6. Population-level use. Estimating how often something occurs requires deliberate epidemiological modelling of the kind researchers used to produce global incidence estimates for leishmaniasis worldwide (PMID 22693548); no comparable estimate exists here for S23 exposure or for harms associated with it.
7. Guideline-grade synthesis. Clinical guidance is normally built by systematic review, as in a 2023 systematic review and guideline for management of scrotal inguinal hernias (PMID 38312421); no such synthesis exists for S23, because the underlying trials that a review would pool have not been published.

How to Read Future S23 Claims

Three habits travel well. First, ask for the primary source — a PMID, a journal and a year — and check that the cited paper actually studied the compound named in the claim. Second, ask what was measured and against what reference, in the way a diagnostic study benchmarks a new readout against biopsy (PMID 35466506) or compares stratification performance in a defined patient group (PMID 35962809). Third, notice when a claim names a mechanism but no outcome, or an outcome but no mechanism; strong evidence usually connects the two, as in the target-and-endpoint design researchers used in the MRPS7-23 and cisplatin study (PMID 41522354).

This course will be revised if primary S23 literature enters the verified evidence set. Until then, the accurate summary is short: S23 is an unapproved, research-use-only non-steroidal compound of the SARM class, and the published record available here does not describe its pharmacokinetics, its effects or its adverse events. Again, this page is educational only and is not medical advice; questions about any substance belong with a licensed physician.

References

• [A new flavan-3-ol from Sargentodoxae Caulis] (Zhongguo Zhong Yao Za Zhi, 2024)
• Molecular Cages Self-Assembled by Imine Condensation in Water (Angewandte Chemie International Edition, 2021)
• Co-targeting MRPS7-23 synergistically enhances cisplatin efficacy to suppress nasopharyngeal carcinoma growth and metastasis (International Journal of Biological Sciences, 2026)
• miR-98-5p as a novel biomarker suppress liver fibrosis by targeting TGFβ receptor 1 (Hepatology International, 2022)
• Hepatic steatosis: Ultrasound assessment using attenuation imaging (ATI) with liver biopsy correlation (Journal of Medical Imaging and Radiation Oncology, 2023)
• Magnetic resonance imaging improves stratification of fibrosis and steatosis in patients with chronic liver disease (Abdominal Radiology, 2022)
• Sequential Fibrosis-4 Index and Mac-2 Binding Protein Glycosylation Isomer Combination Improve Detection of Advanced Fibrosis in Metabolic Dysfunction-Associated Steatotic Liver Disease: A Multicenter Study (Gastro Hep Advances, 2026)
• Cellular microenvironment of erythropoietin-producing cells in hypoxic and injured mouse kidneys (Experimental Physiology, 2026)
• Leishmaniasis worldwide and global estimates of its incidence (PLoS One, 2012)
• Systematic Review and Guidelines for Management of Scrotal Inguinal Hernias (Journal of Abdominal Wall Surgery, 2023)