Peptide & Experimental
Andarine (S-4)
Selective androgen receptor modulator (SARM), not approved · Andarin, S-4, S4, GTx-007, GTX-007, Acetamidoxolutamide
Andarine, usually called S-4 in the scene, is one of the first selective androgen receptor modulators, SARMs for short. In animals it acts strongly in muscle and spares the prostate. In humans, only the basic tolerability from early studies is known so far; an efficacy study is lacking, and the manufacturer abandoned the substance in favor of a successor.
In short
Andarine is a SARM that activates the androgen receptor in a tissue-selective way and builds muscle and bone in animals without placing a heavy load on the prostate. But that is also where the downside lies: like other SARMs, it lowers the body’s own hormone production. In humans there is no published efficacy study, only phase I tolerability data from company statements. Andarine is not approved anywhere, is on the doping list and is sold on the gray market, where the contents are often something other than declared.
What it is
SARM stands for selective androgen receptor modulator. Testosterone acts strongly on muscle and bone, but also on the prostate, the skin and the body’s own hormonal feedback loop. The idea behind SARMs is to build molecules that target the same receptor but with different strength depending on the tissue, with full effect in muscle and little elsewhere.
Andarine carries the laboratory code S-4 or GTx-007 and was developed in the early 2000s at the University of Tennessee and at the company GTx. It was one of the very first representatives of this class, intended as a treatment for muscle wasting, bone loss and cancer-related wasting. Unlike classic anabolic steroids, it is orally active.
How it is supposed to work
Andarine binds to the androgen receptor and activates it. In experiments with castrated rats it restored muscle mass and strength while acting only weakly on the prostate, whereas the comparison hormone dihydrotestosterone more than doubled the prostate. It also increased bone density and reduced body fat percentage. That is the profile SARMs promise.
The same receptor action explains the downside. Like testosterone, andarine signals to the hormonal feedback loop that enough androgen is present, and the pituitary gland suppresses the control hormones LH and FSH. In humans, however, the receptor action of andarine has not been precisely measured in a study; all that is known is a company note on growth activity in the blood.
Chemically, andarine is a molecule with a so-called nitro group. In drug research this structure is considered a possible starting point for liver stress, because reactive intermediates can form during breakdown. This has not been shown for andarine in humans; it is a theoretical warning sign from the structure, not from studies. In rats the substance was absorbed rapidly and completely by mouth and excreted again with a short half-life of around three to five hours.
How far development got
Andarine went through three, later four phase I studies with a total of 86 healthy volunteers. Only the safety and tolerability of single and multiple doses were tested. According to the company, there were no serious side effects, and the results supported once-daily intake.
After that, development ended. The manufacturer licensed the substance to a subsidiary of Johnson & Johnson in 2004, took back the rights in 2006 and decided to develop the structurally related and improved successor ostarine instead of andarine. A planned study on the treatment of cancer-related wasting never began. In the training scene the story circulates that andarine was stopped because of visual disturbances, but no reliable source could be found for this.
What remained was a molecule without approval that found its way onto the gray market. As early as 2008 SARMs were added to the doping list, and in the same year laboratories detected andarine in products declared as green tea extract or moisturizing cream. This shows two things: andarine is really in circulation, and what is on the label often has little to do with the contents.
What is well supported
What is well supported is the pharmacological principle in animals. In castrated and in ovariectomized rats, andarine acted as a full anabolic agonist in muscle and bone while largely sparing the prostate, and it increased bone density in some cases more than dihydrotestosterone. This places andarine among the molecules that established the SARM concept in the first place.
In humans, by contrast, only basic tolerability is documented, and even that only through company statements: in the phase I studies in 86 volunteers no serious side effects occurred, and once-daily dosing was possible. That the SARM principle is alive is shown by further research on muscle wasting and bone loss, important unsolved fields of geriatric medicine. Andarine itself, however, was not pursued further.
What the studies show
Gao et al., Endocrinology 2005 - the animal study on selectivity
Castrated male rats received andarine or dihydrotestosterone for eight weeks. Andarine restored the mass and strength of the soleus muscle and the mass of the levator ani muscle to the level of intact animals, but acted only weakly on the prostate and seminal vesicles, at 16 to 17 percent of control values, whereas dihydrotestosterone more than doubled these organs. The control hormones LH and FSH fell in a dose-dependent manner, and bone density rose.
GTx phase I program - what is known in humans
Three, later four phase I studies with a total of 86 healthy men and women tested only safety and tolerability. According to the company, there were no serious side effects, and the results supported once-daily oral dosing. An efficacy study was not part of this phase. There are no published results of these studies; the information comes from filings with the US Securities and Exchange Commission.
Van Wagoner et al., JAMA 2017 - what is in SARM products
44 products sold online as SARMs were analyzed according to anti-doping standards. Only 52 percent contained any SARM at all, including andarine, and in only 41 percent did the amount match the label. Andarine had previously also been detected in black-market products disguised as green tea extract.
Where the data stop
The decisive gap: for andarine there is no published efficacy study in humans, neither on muscle building nor on fat loss. Everything said about its effect comes from rat experiments or from experience reports. Even the tolerability from phase I is known only through company statements and cannot be read as a scientific paper; reliable figures on side effects in humans are lacking.
The often-heard claim that andarine tints vision yellow or impairs night vision and was abandoned for that reason could not be confirmed in any primary source either. The company documents explicitly state no serious side effects and give as the reason for the end that the improved successor ostarine was preferred. The visual disturbance thus remains an unsupported story. Reliable safety signals in humans so far come only from case reports on the SARM class as a whole.
Status, approval and legal
Andarine is not approved as a medicine anywhere and is not a food supplement; it was never developed beyond phase I. In sport it is prohibited at all times under the WADA Prohibited List 2026, where it is named specifically as andarine among the other anabolic agents. In Germany it is named specifically in the annex to the German Anti-Doping Act, as Andarin (S-4) among the selective androgen receptor modulators. Consequently, acquisition, possession and bringing into the country of non-small quantities for the purpose of doping, as well as trade and supply, are criminal offenses. The US FDA classifies SARMs as unapproved drugs, not as dietary supplements. We do not give dosage information.
Safety
For andarine itself there are hardly any published human safety data beyond basic tolerability. For the SARM class as a whole, by contrast, several cases of drug-induced liver injury, a bilateral Achilles tendon rupture and, in one case, new-onset diabetes under a combination of several substances have been documented. Like other SARMs, andarine suppresses the body’s own hormonal axis in animals. For women the androgenic effect is problematic, and in pregnancy it is ruled out. Anyone with liver disease or cardiovascular risks should stay away from it. And because of the unreliable gray-market quality, when you buy it you do not know what is actually in the bottle.
BK-Score Hype far ahead of evidence
| Human evidence | 2 | |
|---|---|---|
| Mechanism | 5 | |
| Safety data | 3 | |
| Hype gap | 2 | |
| Track record of use | 3 |
Evidence 2, because there is not a single published efficacy study in humans: all efficacy data come from rodents (Gao 2005; Yin 2003; Kearbey 2007), and the three to four completed phase I studies in 86 volunteers are known only through company statements, not published in peer-reviewed form (GTx SEC filings 2003 to 2007). Mechanism 5, because the androgen receptor is a well-established target and tissue selectivity was clearly shown in animals, but andarine’s chain of action in humans has not been quantified - all that is known is a company note on growth activity. Safety 3, because controlled safety data in humans are lacking; there is only unpublished phase I tolerability plus case reports on the SARM class (liver injury, Achilles tendon rupture, one diabetes case under a triple combination), and long-term data are lacking (Vignali 2023; Gould 2021; Sotornik 2022). Hype 2, because andarine is promoted in the scene for definition and fat loss without any human data on this, and because the widespread story of discontinuation due to visual disturbances could not be supported in any primary source - the company information explicitly states no serious side effects and gives as the reason the preference for the successor ostarine. Use 3, because in humans andarine occurs practically only in studies and on the gray market, has no regulatory framework and is prohibited in sport. Direction open, because there are no efficacy data in humans that speak for or against the advertised effect; the animal data support an anabolic effect, and transfer to humans is unresolved.
The score rates the state of knowledge, not the substance. “Safety data 9” means well studied – not harmless.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)
Frequently asked questions about andarine (S-4)
What is andarine?
Andarine, also called S-4 or GTx-007, is one of the first selective androgen receptor modulators. It activates the androgen receptor and in animals acts strongly in muscle but weakly on the prostate. It was developed against muscle wasting and bone loss, but it is not approved anywhere.
Does andarine build muscle?
In rat experiments, yes; there it restored muscle mass and strength. For humans there is no published efficacy study, only experience reports from the training scene. What andarine really does to muscle in humans is scientifically open.
Was andarine stopped because of visual disturbances?
That is a widespread story for which no reliable source could be found. The manufacturer’s documents explicitly state no serious side effects and give as the reason for the end that the improved successor ostarine was preferred. The visual-disturbance reason remains unsupported.
Does andarine lower testosterone?
In animals, yes; it lowered the control hormones LH and FSH in a dose-dependent manner, which indicates suppressed endogenous production. This is considered a typical SARM effect. Exact figures for humans have not been published.
Is andarine legal in Germany?
Andarine is not approved as a medicine and is not a food supplement. It is named specifically in the annex to the German Anti-Doping Act, which is why acquisition and possession of non-small quantities for the purpose of doping are criminal offenses. In sport it is prohibited at all times under the WADA list.
Do andarine products contain what the label says?
Often not. In an analysis of 44 SARM products bought online, only 52 percent contained any SARM at all, and in only 41 percent did the amount match the label. Andarine has also been found in black-market products disguised as tea extract.
Related
- Related topicS-23
- Related topicRAD140 (Testolone)
- Related topicOstarine (enobosarm)
- Related topicCardarine (GW501516)
- Related topicLigandrol (LGD-4033)
- Related topicStenabolic (SR9009)
Sources
- Gao et al., Endocrinology 2005
- Yin et al., Journal of Pharmacology and Experimental Therapeutics 2003
- Kearbey et al., Pharmaceutical Research 2007
- Narayanan et al., Nuclear Receptor Signaling 2008
- GTx, Inc., SEC Form S-1 2003
- Thevis et al., Drug Testing and Analysis 2009
- Van Wagoner et al., JAMA 2017
- Vignali et al., Journal of Xenobiotics 2023
- WADA, Prohibited List 2026
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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-09-27.