At these doses, ostarine provides subtle but real improvements in lean mass retention during cutting and modest anabolic effects during maintenance. The critical difference between SARMs and traditional anabolic steroids is selectivity. Selective androgen receptor modulators occupy a complicated position in the natty plus framework. Bhasin S, Jasuja R. Selective androgen receptor modulators as function promoting therapies. Selective androgen receptor modulator RAD140 is neuroprotective in cultured neurons and kainate-lesioned male rats. Additionally, RAD-140 can help reduce body fat while preserving lean muscle tissue.
Currently osteoporosis is primarily treated with anti-resorptive agents that prevent further breakdown of bone by the body. The ability of SARMs to increase both muscle and bone strength in animal models suggests that they may provide a unique dual approach to osteoporosis therapy (96) (40,42,97)(98). Preclinically, we demonstrated that treatment of ovariectomized mice with SARMs resulted in restoration of the pelvic muscles to their sham-operated weight (95). Since women are highly susceptible to uterine hyperplasia and virilization, steroidal androgens are not an appropriate choice to treat SUI.
Selective androgen receptor modulators (sometimes called specific androgen receptor modulators or SARMs) have been looked at as popular supplements among fitness enthusiasts and chiseled athletes. SARMs have less activity in the prostate and skin than anabolic steroids. Since the levator ani muscle is enriched in the AR, it responds quickly when exposed to androgens. While the results from ER-positive breast cancer trials (one completed and another ongoing) were largely positive, the TNBC trial is still recruiting patients. Currently, to the best of our knowledge, the only SARM that is in clinical trials is enobosarm (GTx, Inc., Memphis, TN). SARMs capable of selectively building pelvic floor muscles with reduced virilizing and uterine proliferative side-effects would be preferred and better tolerated for SUI.
Although strong preclinical data and rationale suggest a positive outcome for a SARM in SUI, the ongoing trial with a SARM for SUI is the first-in-human trial and its outcome will determine the utility of SARMs in SUI. While several other SARMs have been tested clinically for various diseases, they have not advanced beyond phase II proof-of-concept. Other companies that have previously pursued SARMs clinically are Ligand Pharmaceuticals, Merck, Glaxo, and Radius, Inc. Most of the above indicated diseases require prolonged treatment with anabolic agents, which suggests that a strong safety profile will be required. With TNBC being further sub-classified into several subsets, it may be possible that a SARM and an antagonist might provide anti-proliferative effects to distinct subsets of TNBC.
The DNA Binding Domain (DBD) is highly conserved between receptors, has two zinc finger motifs that are responsible for DNA recognition and dimerization, and plays a role in AR binding to Androgen Responsive Elements (ARE) within the regulatory regions of androgen responsive genes. Decades after the discovery of SERMs, Selective Androgen Receptor Modulators (SARMs) (20) were first described and subsequently developed to facilitate tissue-selective activation of the AR. Tamoxifen and raloxifene are classical examples of SERMs that function as antagonists in the breast, but as agonists in the uterus or bone, respectively, either directly or through metabolic conversion (16–19). To circumvent the limitations resulting from global receptor activation, researchers sought ligands, referred to as Selective Receptor Modulators (SRMs) that activate receptors in a tissue-specific manner. As it is ideal to have targeted therapeutic effects, the ubiquitous expression of receptors presents a therapeutic challenge and precludes wider use of exogenous hormone administration. Although both the beneficial and the growth-promoting effects arise from agonistic activities of estrogens, the tissue of action determines whether the effect is beneficial or detrimental.
For most medical applications, an AAS with potent anabolic and minimal androgenic and cardiovascular effects would be an advantage. Anabolic androgenic steroids (AAS) are used to treat a variety of medical conditions, but their side effects have fueled a search for a new class of drugs, with a better separation between desirable anabolic and undesirable androgenic effects. Cardarine (GW ) is a PPAR-delta agonist that enhances fatty acid oxidation and endurance without interacting with the androgen receptor. This effect is consistent with its selective AR agonism in bone tissue and may benefit populations at risk for osteoporosis. Clinical trials at lower doses (1-3 mg) still showed statistically significant lean mass increases, suggesting a dose-dependent anabolic response. In skeletal muscle, MK-2866 robustly activates anabolic signaling pathways including PI3K/Akt/mTOR, increasing muscle protein synthesis and reducing protein degradation via suppression of ubiquitin-proteasome and myostatin pathways. The tissue selectivity of MK-2866 arises from its non-steroidal structure, which produces a distinct AR conformational change compared to testosterone or DHT.
The first preclinical evidence for tissue-selective activation of the AR was that arylpropionamide SARMs increased levator ani muscle weight in castrated rats to the level of sham-operated rats, but only partially increased the prostate and seminal vesicles weight (39,40). Recent clinical trials, although highlighting testosterone’s ability to improve sexual function and muscle mass in older men, corroborated concerns that testosterone’s cardiac risks outweighed its therapeutic benefits (37,38). The AR and its endogenous ligands, androgens, are important for development and maintenance of muscle and bone, secondary sexual organs, and development of other tissues (35). However, virilizing effects and the approval of tamoxifen for treatment of women with advanced breast cancer by the Food and Drug Administration in 1977 caused androgens to fall out of favor. Building on this preclinical foundation, subsequent clinical trials of enobosarm and other SARMs have commonly reported improvements in lean body mass (LBM), which is unsurprising given that SARMs act on the AR. These characteristics — high potency, oral bioavailability, and apparent tissue selectivity — provided the rationale for advancing enobosarm into clinical trials. Obviously, part of SARMs’ tissue selectivity stems from differences in metabolic fate compared with steroidal androgens such as testosterone and DHT.
Dose-dependent increases in strength have been reported anecdotally and are consistent with the compound's mechanism of action as a potent AR agonist in skeletal muscle. Users report meaningful increases in lean mass over 8-12 week cycles at mg/day, though controlled human trial data for this indication is lacking. However, like all exogenous AR agonists, it suppresses endogenous testosterone production through negative feedback on the hypothalamic-pituitary-gonadal (HPG) axis. Importantly, RAD-140 does not undergo aromatization to estrogen and is not a substrate for 5-alpha reductase, meaning it does not produce estrogenic or DHT-mediated side effects.

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