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We are proud to offer S4 in a bottle of 90 capsules with 25mg per capsule.

S4 (Andarine) is a selective androgen receptor modulator (SARM) that has gained attention for its potential therapeutic applications, particularly in the field of muscle wasting conditions and osteoporosis. It is known for its anabolic effects, including increased muscle mass and strength. This article provides an overview of the mechanism of action of S4 Andarine and summarizes key findings from in vitro and in vivo studies.

Mechanism of Action:

S4 Andarine exerts its effects by selectively binding to androgen receptors in the body. Androgen receptors are found in various tissues, including skeletal muscle and bone, and are involved in regulating processes such as protein synthesis, muscle growth, and bone density. By binding to these receptors, S4 Andarine enhances their activity and promotes anabolic effects [1].

Unlike traditional androgenic steroids, S4 Andarine has a high affinity for androgen receptors in skeletal muscle and bone tissue while exhibiting lower affinity for androgen receptors in reproductive organs. This selectivity reduces the risk of androgenic side effects commonly associated with traditional steroids [2].

In Vitro Studies:

In vitro studies have investigated the cellular mechanisms underlying the effects of S4 Andarine. These studies have shown that S4 Andarine effectively binds to androgen receptors, leading to increased protein synthesis and muscle cell hypertrophy. It has been found to be highly selective for androgen receptors in muscle tissue, minimizing potential side effects in other tissues.

Furthermore, S4 Andarine has demonstrated the ability to promote muscle cell differentiation and fusion, which is crucial for muscle growth and repair. It has also been shown to increase muscle satellite cell activity, leading to enhanced muscle regeneration and the development of new muscle fibers.

In Vivo Studies:

Animal studies have been conducted to evaluate the in vivo effects of S4 Andarine on muscle growth, strength, and other physiological parameters.

S4 Andarine has consistently demonstrated anabolic effects in animal models. It has been found to increase lean muscle mass, reduce fat mass, and improve body composition. Additionally, S4 Andarine has shown the potential to enhance muscle strength and physical performance, including endurance and power output [3].

Moreover, S4 Andarine has shown positive effects on bone health. It has been found to increase bone mineral density and improve bone strength, making it potentially beneficial for individuals with osteoporosis or those seeking to improve their bone health.

S4 Andarine and Vision Side Effects:

One notable side effect associated with S4 Andarine is its potential impact on vision. Animal studies have shown that S4 Andarine may bind to androgen receptors in the eyes, leading to temporary visual disturbances, particularly a yellowish tint and difficulty with night vision. These side effects are reversible upon discontinuation of S4 Andarine.

Safety and Side Effects:

While S4 Andarine has demonstrated anabolic effects, it is important to consider its potential side effects and safety profile. In addition to the vision-related side effects, S4 Andarine may also suppress natural testosterone production, leading to hormonal imbalances. Adequate post-cycle therapy and monitoring of hormone levels are recommended to mitigate these potential side effects [4].

It is worth noting that S4 Andarine is prohibited in competitive sports and subject to regulations in many countries. Its use should be approached with caution and under the guidance of healthcare professionals.


S4 Andarine, a selective androgen receptor modulator, has shown potential as a therapeutic agent for muscle wasting conditions and osteoporosis. It selectively targets and binds to androgen receptors in skeletal muscle and bone tissue, leading to increased protein synthesis, muscle hypertrophy, and improved bone health.

In vitro studies have demonstrated its ability to enhance protein synthesis, promote muscle cell differentiation, and increase muscle satellite cell activity.

WARNING: This product is intended for research purposes only. The research chemical designation allows the use of research chemicals strictly for in vitro testing and laboratory experimentation only. Bodily introduction of any kind into humans or animals is strictly forbidden by law.

  1. Yavuz M, Takanlou LS, Avcı ÇB, Demircan T. A selective androgen receptor modulator, S4, displays robust anti-cancer activity on hepatocellular cancer cells by negatively regulating PI3K/AKT/mTOR signalling pathway. Gene. 2023;869:147390. doi:10.1016/j.gene.2023.147390
  2. Gao W, Reiser PJ, Coss CC, 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. doi:10.1210/en.2005-0572
  3. Kearbey JD, Gao W, Narayanan R, 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. doi:10.1007/s11095-006-9152-9
  4. Gao W, Reiser PJ, Coss CC, 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. doi:10.1210/en.2005-0572


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