Andarine (S-4)
1 product from 1 brand · free UK delivery · EU 3–7 days
Andarine, also known as S-4, S4, GTx-007, acetamidoxolutamide and androxolutamide, is a non-steroidal selective androgen receptor modulator (SARM) of the aryl-propionamide family. It was one of the first SARMs to be characterised in detail in animals but never reached later-stage human trials. This page lists every brand of andarine stocked at Free Muscle, compared on strength per capsule, capsules per pack and batch testing, and summarises the published research and its limits.
What is andarine?
Andarine is a synthetic ligand of the androgen receptor (AR) built on the aryl-propionamide scaffold that also produced ostarine and S-23. The scaffold was derived from the anti-androgen bicalutamide by researchers at the University of Tennessee and Ohio State University, who found that small structural changes turned a receptor blocker into a tissue-selective agonist. Andarine behaves as a partial agonist in the prostate and a full agonist in skeletal muscle and bone in animal models, which is the defining SARM profile.
Unlike ostarine, andarine did not progress far in clinical development. GTx investigated it as GTx-007 for benign prostatic hyperplasia and muscle wasting in the mid-2000s, but no controlled human trial results have been published in the peer-reviewed literature and the compound was set aside in favour of ostarine. Andarine has never been approved as a medicine by the MHRA, EMA, FDA or any other regulator. It is widely discussed for a visual side effect, a yellow tint to vision and difficulty adapting to darkness, but this is reported anecdotally: a PubMed search in October 2026 found no published study of andarine and vision.
Identifiers for andarine, checked against PubChem in October 2026:
| Identifier | Andarine (S-4) |
|---|---|
| Chemical name | (2S)-3-(4-acetamidophenoxy)-2-hydroxy-2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]propanamide |
| CAS number | 401900-40-1 |
| Molecular formula | C19H18F3N3O6 |
| Molecular weight | 441.4 g/mol |
| PubChem CID | 9824562 |
What the published research reports
Muscle, bone and pituitary effects in castrated rats (2005). Gao and colleagues treated castrated male rats with S-4, dihydrotestosterone (DHT) or vehicle for eight weeks. S-4 restored soleus muscle mass and strength and levator ani muscle mass to the levels seen in intact animals, matching DHT. Where DHT more than doubled prostate and seminal vesicle weights relative to intact controls, S-4 returned them to only 16 and 17 per cent of control. S-4 also increased total body bone mineral density more than DHT and suppressed plasma LH and FSH in a dose-dependent manner, indicating agonist activity in the pituitary.
Bone loss and body fat in ovariectomised rats (2007). Kearbey and colleagues treated 120 female rats for 120 days after ovariectomy. S-4 maintained whole-body and trabecular bone mineral density and cortical content, increased femoral bone strength on biomechanical testing and reduced body fat, in a model of accelerated bone loss.
Pharmacokinetics in rats (2004). Kearbey and colleagues gave S-4 intravenously and orally to male rats across a range of doses. Clearance was slow, the half-life was between 2.6 and 5.3 hours, and oral bioavailability was complete at the lower doses and dose-dependent above that.
UK market analysis of SARM products (2021). Leaney and colleagues, working in a UK laboratory, analysed supplement products marketed as SARMs to UK consumers. Findings ranged from products with no active ingredient to products containing undeclared prohibited substances, and where a SARM was present its concentration frequently did not match the label.
All of the andarine efficacy data above come from rats. There are no published controlled human trials, and none of these findings is a claim about the products listed on this page.
Brands of andarine we stock
- iMuscle Andarine S-4, 15mg, 60 capsules. Capsule form, 900mg of compound per pack. A certificate of analysis is shown on the listing only where iMuscle has supplied one for the batch we hold; if none is displayed, none is available for that batch. View the iMuscle Andarine listing.
Free Muscle does not currently produce its own andarine, so there is no Janoshik-assayed Free Muscle batch on this page at present. Any Free Muscle-brand line added later will carry batch-level Janoshik testing like the rest of our range.
How to compare them
Multiply strength per capsule by capsules per pack to get total milligrams (15mg by 60 gives 900mg). Divide the pack price by that figure for cost per milligram, which is how a 15mg pack is compared fairly against a 25mg or 50mg pack from another supplier. Then weigh the certificate. Market analyses of SARM products, including the 2021 UK study above, have repeatedly found labels that do not match contents, so a batch-specific COA from an independent laboratory is the only way to know what a pack contains. Our guide to price per milligram covers the arithmetic.
Batch testing and certificates of analysis
Of the three aryl-propionamide SARMs we list, andarine is the only one with a nitro group, and it also carries an acetamido group where ostarine has a second cyano group. Its certificate should therefore report an identity consistent with C19H18F3N3O6 and a molecular weight of 441.4, well apart from ostarine at 389.3, so mass spectrometry separates the two easily. After identity, check the purity or content figure, the batch number against your bottle, the laboratory name and the test date.
Janoshik Analytical tests every Free Muscle-brand batch, with the certificate emailed on request. The andarine here is made by iMuscle, and a certificate is displayed on its listing only when iMuscle has provided one for the batch in stock. The lab tests page describes the checks in more detail.
Legal status in the UK
No UK regulator has authorised andarine for any human use. No MHRA marketing authorisation has ever been granted for it, which means it is not a licensed medicine, and according to UK Anti-Doping's SARMs warning (updated April 2026) the Food Standards Agency classes SARMs as unauthorised novel foods that cannot lawfully be sold or advertised as food or as an ingredient of a food supplement. The Misuse of Drugs Act 1971 does not list andarine, so it is not a controlled drug either. Free Muscle sells it for laboratory and research purposes only, never for human consumption, and only to buyers aged 18 or over. The 2026 WADA Prohibited List names andarine in section S1.2, other anabolic agents, and prohibits it at all times, in and out of competition. Our research guide to SARMs covers the wider class.
Storage and handling
Andarine is supplied as capsules in a sealed bottle. Leave them in that bottle rather than moving them to another container, protect it from heat, damp and direct light, and note the lot number before the label wears. Store it where children and animals cannot reach it, and dispose of surplus through a chemical waste route.
Delivery and returns
Orders are sent from our UK operations in Scunthorpe, with free tracked delivery to UK addresses and plain packaging. Same-working-day processing applies to orders placed before 2pm, Monday to Friday, and EU delivery takes 3 to 7 working days. Unopened items are returnable within 30 days. We sell only to customers aged 18 or over. Details are on the shipping page and the guarantee page.
Related reading
- Ostarine (MK-2866): what the clinical trials found and UK status, the closest relative with human trial data
- What are SARMs? The 2026 research guide
- SARMs explained: how selective androgen receptor modulators work
- How to read a certificate of analysis
- How to choose a SARMs or peptide supplier in the UK: a checklist
Related collections: Ostarine (MK-2866), S-23, iMuscle, all SARMs.
References
- Gao W, et al. Selective androgen receptor modulator treatment improves muscle strength and body composition and prevents bone loss in orchidectomized rats. Endocrinology. 2005;146(11):4887-4897. PMID: 16099859.
- 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):328-335. PMID: 17063395.
- Kearbey JD, et al. Pharmacokinetics of S-3-(4-acetylamino-phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamide in rats, a non-steroidal selective androgen receptor modulator. Xenobiotica. 2004;34(3):273-280. PMID: 15204699.
- Leaney AE, et al. Analysis of supplements available to UK consumers purporting to contain selective androgen receptor modulators. Drug Test Anal. 2021;13(1):122-127. PMID: 32748554.
- 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):2245-2254. PMID: 20623476.
- Grata E, et al. SARM-S4 and metabolites detection in sports drug testing: a case report. Forensic Sci Int. 2011;213(1-3):104-108. PMID: 21816554.
- Van Wagoner RM, et al. Chemical Composition and Labeling of Substances Marketed as Selective Androgen Receptor Modulators and Sold via the Internet. JAMA. 2017;318(20):2004-2010. PMID: 29183075.
Last reviewed: October 2026.
Research compounds sold by Free Muscle are supplied for laboratory research use only and are not for human consumption. They are not authorised as medicines by the MHRA, EMA or FDA, are not food supplements, and are sold only to adults aged 18 or over. Nothing on this page is medical or dosing advice. Summaries of published research describe study findings and are not claims about any product.
Frequently asked questions
Is andarine legal in the UK?
Andarine is not a controlled drug in the UK, but there is also no permission to sell it for people to take. It holds no MHRA marketing authorisation and is not an authorised food supplement, so any sale or labelling for human consumption would be unlawful. We supply andarine to adults for laboratory research only, and customers must be 18 or over.
Is andarine a SARM or a steroid?
It is a SARM, not a steroid. Andarine's aryl-propionamide structure was developed from bicalutamide, a drug that blocks the androgen receptor, and small changes turned it into an activator. In castrated rats it acted only partially on the prostate while restoring muscle and bone, and it lowered the pituitary hormones LH and FSH (Gao 2005). It has no steroid ring system, WADA lists it among anabolic agents, and it has never been approved as a medicine.
What is the difference between andarine and ostarine?
Both are aryl-propionamide SARMs from the same academic programme, and they differ at two points in the molecule: the nitro group on one ring of andarine is a cyano group in ostarine, and andarine's acetamido group on the other ring is a second cyano group. That lowers the molecular weight from 441.4 to 389.3. Ostarine went on to phase 2 and phase 3 human trials, while andarine has no published controlled human trial. Reports of visual disturbance concern andarine.
Has andarine been tested in humans?
No controlled human trial results for andarine have been published in the peer-reviewed literature. GTx investigated it in the mid-2000s but shifted development to ostarine. The published efficacy data come entirely from rat studies of muscle, bone, prostate and body composition. There are no human data on long-term effects or on the visual side effect reported anecdotally.
How do I verify a batch of andarine?
iMuscle supplies the andarine on this page, and any certificate of analysis for the batch we hold is shown on the listing itself. There is no email request route for third-party brands, because we can only share what the manufacturer has issued. When a certificate is displayed, confirm the lot number against your label and read the identity and content lines. Our guide to reading a COA explains what each figure means.
Is andarine detectable in sports drug testing?
Yes. It is banned at all times: section S1.2 of the 2026 WADA Prohibited List covers andarine. Its urinary metabolites were characterised as targets for routine doping control (Thevis 2010), and in 2010 the Swiss doping laboratory reported what it described as the first SARM case found in in-competition testing, which involved S-4 (Grata 2011). Andarine was also among the three SARMs detected when 44 products sold online were analysed in 2017. Anyone subject to anti-doping rules should treat it as prohibited.
Which strength of andarine should I choose?
That is not a question we answer. Andarine is sold for laboratory research only, so strength, quantity and use are matters for the research protocol rather than for us. What we do publish is the strength per capsule (15mg) and capsules per pack (60) so that total content and cost per milligram can be compared with other listings. Nothing here is dosing or medical advice.
Does andarine affect vision, and what side effects have been reported?
There is no published human trial of andarine, so there are no controlled data on side effects in people. Accounts of yellow-tinted vision and poor vision in the dark are anecdotal; a PubMed search in October 2026 found no published study of them. In castrated rats, andarine lowered the pituitary hormones LH and FSH (Gao 2005), and products sold to UK consumers as SARMs did not reliably contain what their labels stated (Leaney 2021).