Andarine S-4 — 60 caps, 15mg

iMuscle Andarine S-4 is supplied as 60 capsules stated at 15 mg each, for a total of 900 mg of andarine per pack. Andarine (S-4) is an early non-steroidal selective androgen receptor modulator whose published evidence comes from animal studies. The product is manufactured by iMuscle and stocked by Free Muscle for laboratory research by adults, with free tracked UK delivery.

About Andarine (S-4)

Andarine, usually written S-4 or S4 and coded GTx-007 during development, is one of the earliest non-steroidal selective androgen receptor modulators. It came from the aryl-propionamide series developed at the University of Tennessee and GTx Inc. in the early 2000s. Like testosterone, it binds and activates the androgen receptor. The series aimed at action on muscle and bone with less effect on other androgen-sensitive tissue; for andarine, that aim was tested only in animals.

The published data for S-4 are preclinical. In a 2007 study of 120 female rats, ovariectomised to model accelerated bone loss and treated for 120 days, S-4 maintained whole-body and trabecular bone mineral density and cortical bone content, increased the strength of the femur on mechanical testing and reduced body fat (Kearbey et al., 2007). No controlled human trial of andarine has been published, and the development programme was discontinued. In informal reports the most frequently described effect is a yellow tint to vision and slower adaptation to darkness, attributed in those accounts to the molecule binding in the retina; that finding has not been characterised in a clinical study.

Andarine has never been approved as a medicine and is named under section S1.2 of the WADA Prohibited List. The animal findings summarised here are not claims about this product.

Chemical identity

These PubChem identifiers define the substance a certificate for this pack should report. The (2S) marks the molecule's single stereocentre.

• Systematic name: (2S)-3-(4-acetamidophenoxy)-2-hydroxy-2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]propanamide
• CAS number: 401900-40-1
• Formula and molecular weight: C19H18F3N3O6, 441.4 g/mol
• InChIKey: YVXVTLGIDOACBJ-SFHVURJKSA-N
• PubChem CID: 9824562

This listing

• Compound: Andarine (S-4)
• Brand: iMuscle
• Form: capsules
• Pack size: 60 capsules
• Stated strength: 15 mg per capsule (manufacturer's label claim)
• Stated total per pack: 900 mg
• Intended use: laboratory research only, not for human consumption
• Sold to adults aged 18 and over

The strength is the manufacturer's label claim; only a batch certificate confirms it. To compare brands of Andarine, use total milligrams per pack, as explained in price per milligram.

Andarine in the UK: buying, legal status and what to check

Behind searches such as "andarine UK", "S4 SARM UK" and "S4 SARM for sale" sit two questions: can andarine lawfully be bought here, and what makes a listing checkable rather than something taken on trust.

The legal position

Andarine is not a licensed medicine in the UK: it has no MHRA marketing authorisation, is not an authorised food supplement, and cannot lawfully be sold for human consumption. Nor is it a controlled drug under the Misuse of Drugs Act 1971. Free Muscle supplies it to adults aged 18 or over for laboratory research only. It is prohibited at all times under section S1 (anabolic agents) of the WADA Prohibited List. Buyers are responsible for the rules that apply to them, including any anti-doping code and, for orders sent to the EU, their own country's import rules. Background on the class is in What are SARMs? The 2026 research guide.

What a checkable listing shows, and how this one measures up

A listing without an amount per capsule fails the first check: it can be neither priced per milligram nor compared with an assay.

This matters for andarine in particular. In 2009 anti-doping researchers at the German Sport University Cologne found andarine in oily liquids sold online as green tea extract and face moisturiser, and described the case as the first proof that SARMs were being sold and misused without any clinical approval (Thevis et al., 2009). Only analysis revealed what those bottles held; reviews and Reddit threads about "S4" record experiences, not contents. More checks are in how to choose a SARMs supplier in the UK.

Capsules compared with other forms

Three formats are sold under the andarine name: capsules, liquids and loose powder. Chemically they are identical; they differ in where the quantity per unit gets fixed and in how anyone can verify it. We know of no published comparison of andarine formats.

• Capsules (this product). Powder is blended and filled into shells at manufacture, so the 15 mg per capsule is set before the pot is sealed and a certificate can measure it directly. The limit is uniformity: an assay of pooled capsules reports their average, and variation between capsules shows only if units are tested one by one.
• Liquids. Labelled by concentration, so any portion is only as accurate as the volume measured. Solvent evaporating from a bottle opened repeatedly concentrates what remains, and a dissolved compound can come out of solution in the cold, so a certificate describes the liquid only as it was when sampled.
• Loose powder. Sold by weight, which places accuracy entirely on the balance and handling of the laboratory using it.
• Injection. Sometimes asked about by analogy with peptides. Andarine is a small synthetic molecule, not a peptide, so the objection raised against swallowed peptides, breakdown by digestive enzymes, does not apply in the same way (see do oral peptides work). No published human study has given andarine by injection or any other route.

On stability, dry powder sealed in a capsule is kept away from the solvents and water in which chemical breakdown usually proceeds fastest. That is a general principle, not a measured result: we know of no published shelf-life data for andarine in any format.

Andarine compared with ostarine

"Andarine vs ostarine" is the comparison searched most often for this compound, and the two are close relatives: aryl-propionamide SARMs from the same GTx programme, built on the same (2S)-2-hydroxy-2-methylpropanamide backbone with a trifluoromethyl group on the anilide ring. They differ in two substituents, and in how far each went in development.

The real difference is depth of evidence. Ostarine's trials enrolled people under medical supervision and published what they measured, adverse events included; that record and its limits are set out in Ostarine (MK-2866): the most-studied SARM, what trials found. Andarine has no equivalent, so claims that it is "stronger" or "milder" than ostarine in people rest on anecdote. Milligrams do not translate either: andarine is the heavier molecule, so equal figures on two labels are not equal amounts of substance, and no study establishes any equivalence between them.

In law and in sport there is no difference, and both are sold here for laboratory research only. Ostarine brands, including iMuscle Ostarine, are compared in the Ostarine (MK-2866) collection.

Reading the certificate of analysis for this product

iMuscle is a third-party brand, so any certificate of analysis (COA) for this pack is the manufacturer's, not ours. Where iMuscle supplies a COA for the batch we hold, we show it; where none exists for the batch in stock, we say so rather than show a generic document. Free Muscle-brand compounds are assayed batch by batch at Janoshik Analytical; that programme does not cover iMuscle. A real andarine batch certificate should answer each point below.

1. Which compound. Andarine, S-4 or GTx-007, ideally with CAS 401900-40-1. A document headed only "SARM" says nothing about this pot.
2. Identity, and by what method. HPLC matches the sample's retention time to a reference standard; LC-MS adds a molecular mass that should fit C19H18F3N3O6 (441.4 g/mol). The 2009 Cologne analysis confirmed identity against reference material by both liquid chromatography and high-resolution mass spectrometry (Thevis et al., 2009).
3. Purity. Usually an HPLC area percentage: the share of detected material that is andarine. It is the line that would expose a by-product like the one in that 2009 sample, left by poor purification at roughly a tenth of the andarine present. It says nothing about milligrams per capsule.
4. Content per capsule. The assayed milligrams in a capsule, the figure that tests the 15 mg claim. If it is missing, so is any check on the 900 mg total.
5. Stereochemistry. Andarine is the (2S) form. Its (2R) mirror image has the same formula and mass and is not separated by standard HPLC; only a chiral method tells them apart. A certificate silent on this has not tested for it.
6. Lot number, test date and laboratory. The lot on the report has to be the lot on your pot; the test date tells you how old the result is; and the issuing laboratory, if named, can be asked whether the report is genuine.

Any blank line means the matching label figure is still unverified; contact us and we will tell you what documentation exists for the stock we hold. See also how to read a COA and our lab tests page.

Detection, sport and testing

Andarine is named in section S1.2 (other anabolic agents) of the WADA Prohibited List and is banned in and out of competition; WADA has prohibited SARMs as a class since 2008 (Thevis et al., 2010). Anti-doping rules apply strict liability: an athlete is responsible for any prohibited substance in their sample, whatever its source, a mislabelled product included.

Testing does not depend on finding the unchanged molecule. The same Cologne group then characterised andarine's urinary metabolites by liquid chromatography with high-resolution mass spectrometry and confirmed targets for routine doping control: glucuronic acid conjugates of andarine and of its hydroxylated or deacetylated products, a hydrolysis product formed when one of its two aromatic rings is removed, and sulfate conjugates of the hydroxylated and deacetylated metabolites (Thevis et al., 2010).

What the published record does not give is a detection window. We know of no verified study reporting how long andarine or its metabolites remain detectable, so for this product the accurate statement is: detectable, window not established. The absence of a figure is not evidence of a short window. Anyone subject to anti-doping rules should treat any contact with andarine as a risk of an adverse analytical finding.

Storage, stability and handling

We know of no published stability study of andarine capsules, so the expiry or best-before date printed by iMuscle is the working limit, and a certificate describes the batch as it was on its test date, not as it is now.

• Container. Leave the capsules in the pot they came in and close it after every opening. Separated from that pot and its lot number, capsules can no longer be matched to a certificate.
• Conditions. A cool, dry cupboard away from direct light and from radiators, ovens and sunny windowsills. Steam from bathrooms and kitchens softens capsule shells and makes powder clump.
• Records. Write the opening date next to the lot number. Any portion taken for analysis needs its own label giving compound, lot and date.
• Changes in appearance. Capsules that have discoloured, softened or stuck together are no longer the material a certificate describes; set them aside and contact us with the lot number.
• Handling and disposal. Wear gloves for opened capsules or powder, work away from food and drink, keep the pot out of reach of children and pets, and dispose of unwanted material as chemical waste under local rules, never in household bins or drains.

Glossary

• SARM: selective androgen receptor modulator; a non-steroidal ligand of the androgen receptor, pursued in the hope of anabolic action in muscle and bone with less action on the prostate.
• Androgen receptor: the protein inside cells that testosterone and dihydrotestosterone activate.
• Aryl-propionamide: the chemical family of andarine, ostarine and S-23, in which a propanamide chain links two substituted benzene rings.
• Preclinical: research in cells or animals, before or instead of trials in people.
• Ovariectomised rat: a female rat with the ovaries removed, a standard model of bone loss after oestrogen deficiency.
• Bone mineral density: mineral content of bone per unit of area or volume, measured in the 2007 study by dual-energy X-ray absorptiometry.
• Enantiomers: two mirror-image forms of a molecule with a stereocentre, such as (2S)- and (2R)-andarine.
• HPLC: high-performance liquid chromatography, which separates a sample's components for identification and measurement against a standard.
• LC-MS: liquid chromatography coupled to mass spectrometry, adding each component's mass for a stronger identity check.
• Metabolite: a breakdown or conversion product formed in the body; some persist longer than the parent molecule, which is why testers look for them.
• Glucuronide: a metabolite formed when the body attaches glucuronic acid to a molecule, easing its excretion in urine.

Related

• All brands of Andarine (S-4), compared on strength, pack size and batch testing
• All iMuscle products stocked at Free Muscle
• Ostarine (MK-2866), S-23 and all SARMs
• Delivery and returns

This product is supplied for laboratory research use only. It is not a medicine, has not been evaluated by the MHRA, EMA or FDA, and is not for human consumption. Sold to adults aged 18 and over. Nothing on this page is medical, dosing or usage advice.

References

1. Kearbey JD, et al. Selective Androgen Receptor Modulator (SARM) treatment prevents bone loss and reduces body fat in ovariectomized rats. Pharm Res. 2007;24(2):328-35. PMID: 17063395.
2. Thevis M, et al. Detection of the arylpropionamide-derived selective androgen receptor modulator (SARM) S-4 (Andarine) in a black-market product. Drug Test Anal. 2009;1(8):387-92. PMID: 20355219.
3. Thevis M, et al. Mass spectrometric characterization of urinary metabolites of the selective androgen receptor modulator andarine (S-4) for routine doping control purposes. Rapid Commun Mass Spectrom. 2010;24(15):2245-54. PMID: 20623476.