RAD 140, also known as Testolone, is not a steroid. It is a nonsteroidal selective androgen receptor modulator, or SARM. While it activates some of the same receptors that steroids do, its chemical structure, how it behaves in the body, and its effects on different tissues are fundamentally different from anabolic-androgenic steroids like testosterone or nandrolone.
That said, the line between “steroid” and “not a steroid” matters less than most people think. RAD 140 carries serious health risks, is not approved for human use, and is banned in competitive sports. Here’s what you need to know.
Why RAD 140 Isn’t Technically a Steroid
Anabolic-androgenic steroids share a distinctive molecular backbone: four interconnected carbon rings known as the steroid nucleus. Testosterone, nandrolone, stanozolol, and other classic steroids all have this structure. RAD 140 does not. Its chemical structure is built around an oxadiazole ring system with attached benzonitrile groups, making it a completely different class of molecule. The original research team that developed it at Radius Health explicitly classified it as a “nonsteroidal” SARM when they published their findings in ACS Medicinal Chemistry Letters.
Most SARMs on the market, including ostarine and ligandrol, are also nonsteroidal. A rare exception is YK11, which does contain a steroidal backbone. RAD 140 is not one of those exceptions.
How It Differs From Steroids in the Body
The key difference isn’t just the shape of the molecule. It’s what happens after you take it. Traditional anabolic steroids are full agonists of androgen receptors, meaning they activate those receptors aggressively across every tissue that responds to androgens: skeletal muscle, bone, prostate, skin, liver, and the central nervous system. They don’t pick and choose. Many steroids also get converted into other hormones through enzymes in the body. One enzyme (5-alpha reductase) converts testosterone into a more potent form that amplifies effects in the prostate and skin, contributing to prostate enlargement, acne, and hair loss. Another enzyme (aromatase) converts steroids into estrogen, which can cause breast tissue growth in men.
SARMs like RAD 140 are designed to be more selective. Preclinical data shows they act as partial or tissue-selective agonists, promoting activity in muscle and bone while producing weaker activation in the prostate and other androgen-sensitive tissues. RAD 140 is not a substrate for 5-alpha reductase or aromatase, so it avoids those metabolic conversions that cause many of the classic steroid side effects.
“Selective” is the operative word, but it comes with an important caveat: selectivity is relative, not absolute. The tissue-selective profile seen in animal studies doesn’t mean RAD 140 is safe or side-effect-free in humans.
It Still Carries Serious Health Risks
Despite not being a steroid, RAD 140 can cause significant harm. Liver damage is the most well-documented concern. A case published in The American Journal of Gastroenterology describes a 29-year-old man with no prior health problems who developed severe drug-induced liver injury after taking RAD 140 for a few months. He showed up to the emergency department with jaundice and lethargy, and his bilirubin levels (a marker of liver function) initially worsened even after he stopped the supplement, peaking at 42 mg/dL before slowly improving. His doctors ruled out alcohol, acetaminophen, viral hepatitis, autoimmune conditions, and iron overload. The only explanation was RAD 140. Recovery took months, and the medical team noted that acute liver failure requiring a transplant is always a possibility in these cases. Liver values can take three to five months to normalize.
The FDA has issued a broader warning about SARMs as a class, linking them to increased risk of heart attack or stroke, psychosis and hallucinations, sleep disturbances, sexual dysfunction, infertility, testicular shrinkage, and pregnancy miscarriage. These aren’t theoretical risks pulled from animal studies. They come from reports and post-marketing surveillance of real users.
Legal and Regulatory Status
RAD 140 is not FDA-approved for any purpose. It has reached only Phase 1 clinical trials in humans, where it was being studied as a potential treatment for hormone receptor-positive breast cancer in postmenopausal women. Phase 1 trials are the earliest stage of human testing, focused on basic safety and tolerability rather than proving the drug works. No SARM has completed the full approval process.
Despite this, RAD 140 is widely sold online, often labeled as a “research chemical” or marketed alongside dietary supplements. The FDA considers SARMs unapproved drugs. They cannot be legally marketed in the United States as either dietary supplements or medications. Products sold this way are skirting regulatory boundaries, and their contents are unverified. You have no guarantee that what’s on the label matches what’s in the bottle.
In competitive sports, the distinction between SARMs and steroids is irrelevant. The World Anti-Doping Agency lists SARMs under section S1.2 of its prohibited list, categorized as “Other Anabolic Agents” alongside traditional steroids. RAD 140 is specifically named. USADA enforces the same rules for athletes in the United States. A positive test for RAD 140 carries the same consequences as testing positive for testosterone or any other banned anabolic agent.
Why the Steroid Question Matters Less Than You Think
People asking whether RAD 140 is a steroid are often trying to gauge how risky it is. The implicit assumption is that if it’s “not a steroid,” it might be safer or more acceptable. That’s a misleading framework. RAD 140 suppresses your natural testosterone production, can damage your liver, and has never been proven safe for human use at any dose. The nonsteroidal label means it has a different chemical structure and a somewhat different mechanism of action. It does not mean it’s gentle, legal, or well-understood.
The only completed human trial was a Phase 1 dose-escalation study in cancer patients. There are no published long-term safety data in healthy adults. Every person using RAD 140 for bodybuilding or athletic performance is essentially running an uncontrolled experiment on themselves with a compound that has less clinical data behind it than most prescription drugs have before they even reach Phase 2 trials.