RAD-140 + YK-11

RAD-140 plus YK-11 refers to a combination, or stack, of two selective androgen receptor modulators (SARMs) commonly sold together to bodybuilders and athletes seeking increases in muscle mass and strength ^[1]. SARMs are a class of compounds that bind the androgen receptor, the same receptor activated by testosterone, but were designed to favor anabolic effects in muscle and bone over the androgenic effects on the prostate and other tissues; despite active pharmaceutical research into conditions such as muscle wasting, cachexia, and sarcopenia, no SARM has received full clinical approval ^[1].

RAD-140, also called Testolone, is a nonsteroidal SARM originally developed as a potent, orally active androgen receptor agonist ^[1]. YK-11 is chemically different: it is a steroidal SARM built on a dihydrotestosterone-like steroid nucleus, and it is widely promoted to bodybuilders as a myostatin inhibitor, though that popular claim rests on limited laboratory research rather than human evidence ^[1][7]. Because the two compounds are thought to act on muscle through complementary androgen-receptor pathways, they are frequently combined in an effort to maximize gains, which is the basis for this paired entry.

Neither compound is approved by the United States Food and Drug Administration or any comparable regulator, and both have been on the World Anti-Doping Agency Prohibited List since SARMs were added in 2008, making them banned in essentially all competitive sport ^[1]. They are sold as research chemicals or mislabeled dietary supplements, and analytical surveys have repeatedly found SARMs including YK-11 present in supplements, sometimes undisclosed on the label and at widely varying concentrations; YK-11 in particular is chemically unstable ^[8]. They are usually encountered as capsules or as liquid solutions for oral use. The combination of unproven efficacy, no regulatory oversight, and documented serious adverse events makes this an especially high-risk category ^[1][8].

The combo has no human study behind it and stacks the risks of both compounds. RAD-140 strongly suppresses natural testosterone and has real-world reports of drug-induced liver injury; YK-11 adds its own liver concern given its methylated steroid-like structure. Expect lower HDL cholesterol and the need for a hormone-recovery plan afterward. Neither is approved, both are banned by WADA, and products are unregulated with uncertain content. The liver and hormonal load is the main reason to be cautious. Not for human use.

This stack pairs two separately developed research chemicals. RAD-140, also called Testolone, was discovered by the biopharmaceutical company Radius Health and first described in the scientific literature around 2011 as a potent nonsteroidal selective androgen receptor modulator intended for conditions such as muscle wasting and, in later work, hormone-receptor-positive breast cancer. YK-11 was synthesized by the Japanese researcher Yasuhiro Kanno and colleagues, also reported around 2011, as a steroidal SARM with a dihydrotestosterone-like structure that showed follistatin-related, myostatin-modulating activity in cell culture.

Neither compound has ever been approved for human use, and both entered the bodybuilding and research-chemical markets rather than clinical practice. The practice of stacking the two arose within fitness communities seeking combined anabolic signals, not from any formal drug-development program. Both agents are prohibited in sport by the World Anti-Doping Agency, and the pairing has no legitimate regulatory or clinical history.

Within bodybuilding circles the RAD-140 and YK-11 stack has a strong reputation for producing rapid gains in muscle mass and strength, and RAD-140 in particular is often described by users as one of the more potent SARMs available. That enthusiasm, however, must be weighed against a sobering safety record and a striking absence of human evidence. No controlled clinical trials have shown that either compound safely builds muscle in people, and much of YK-11's myostatin-inhibiting reputation rests on limited in-vitro work rather than human data.

More seriously, RAD-140 has been linked in published medical case reports to drug-induced liver injury and to serious cardiovascular events in young users, and a long-term rodent study found it increased frailty and mortality rather than improving strength. Products sold as SARMs are also frequently mislabeled or adulterated. In honest terms, the anabolic appeal of this stack is real to its users, but its benefits remain unproven and its documented risks are substantial.