Ostarine is one of the better-known SARMs sold online to people hoping to build muscle, lose fat or improve their performance. You might see it promoted as an alternative to anabolic steroids, sometimes with claims that it provides similar benefits with fewer risks. The evidence doesn’t support that kind of certainty. There is human research on ostarine, but a lot of it has been conducted in older adults or people with illnesses that can cause muscle loss. The results from these studies have limited relevance for a healthy person considering the use of ostarine for enhancing their appearance or performance. Here’s what you need to know about ostarine in Australia, its side effects and risks.
What is ostarine?
Ostarine is the common name for enobosarm, also known as MK-2866.
It belongs to a group of drugs called selective androgen receptor modulators, or SARMs. These drugs act on androgen receptors, which respond to hormones such as testosterone, and other androgenic hormones. SARMs were developed with the aim of producing useful effects in tissues such as muscle and bone while limiting unwanted effects elsewhere in the body, such as the prostate and skin.
That idea is one reason SARMs have attracted interest for conditions involving muscle loss. It has also helped drive their popularity among people hoping for muscle and performance benefits.
Being designed to act selectively doesn’t guarantee that a drug is free from significant side effects.
Does ostarine build muscle?
Ostarine can increase lean body mass in men aged over 60 and postmenopausal women, and in people with cancer cachexia (a syndrome of weight loss, anorexia, loss of muscle mass, inflammation, insulin resistance and functional decline).
These findings are often used to promote ostarine as a muscle-building drug. But there are two important catches.
First, an increase in lean body mass does not mean that there is an increase in muscle mass.
Second, the effect of ostarine in elderly people, and others with advanced cancer and associated wasting, is not a reliable indicator of effects in younger, healthy people who might take ostarine for appearance or performance gains.
So while ostarine can affect body composition in older adults and cancer patients with wasting disease, there isn’t evidence establishing it as a safe and effective way for healthy people to build muscle or improve athletic performance.
Does ostarine burn fat?
Ostarine is not a proven safe and effective weight loss drug.
Reductions in fat mass observed in studies of older adults and people with cancer cachexia do not mean that ostarine is useful for fat-burning or ‘cutting’ in younger, healthy individuals.
What are the risks of taking ostarine?
The long-term safety of ostarine use hasn’t been established. Adverse effects of SARMs include:
Specific adverse events associated with ostarine use include liver damage, sexual dysfunction and gynaecomastia.
Unregulated substances haven’t been assessed by the TGA for safety, quality and effectiveness. They may contain a different amount of an active ingredient than the label states, an undeclared ingredient, no active ingredient or contaminants.
A label saying ‘research chemical’ or ‘not for human consumption’ isn’t evidence that the product is safe or accurately labelled.
Is ostarine legal in Australia?
Ostarine is a prescription-only substance in Australia.
No SARM medicine is currently approved by the TGA for human use. That means ostarine sold online shouldn’t be treated like an ordinary sports supplement simply because it can be purchased from a website.
Australian rules also apply to the import, supply and possession of prescription medicines and other therapeutic goods. If you’re considering buying a product from overseas, check the current TGA requirements rather than relying on what the seller says about its legal status.
Is ostarine banned in sport?
Yes.
Ostarine is specifically listed as a prohibited SARM in the 2026 WADA Prohibited List. It is prohibited at all times for athletes covered by WADA anti-doping rules, not just during competition.
This is also relevant to products that don’t list ostarine on their label. Unregulated products can contain undeclared ingredients, so athletes need to consider the anti-doping risk as well as the health risk.
Is ostarine a steroid?
No. Ostarine isn’t an anabolic steroid.
It is a SARM, which means it acts on the androgen receptor. That shared pathway helps explain why SARMs are sometimes marketed as alternatives to anabolic steroids.
The distinction doesn’t make ostarine a risk-free option. ‘Not a steroid’ and ‘safe’ are two different claims.
What should you do if you’re considering ostarine?
If you’re thinking about using ostarine to gain muscle, change your body composition or improve performance, it’s worth separating what you want to achieve from the claims being made about the drug.
A GP or sports physician can help you look at evidence-based ways to work towards your goal and discuss potential health risks without relying on the claims from people or businesses selling a product.
If you’re already using ostarine, tell your doctor what you’re taking. Give them the product name and, if possible, information about where it came from. Don’t assume that an online product contains exactly what its label says. Evidence that ostarine can change lean body mass in specific research studies of selected participants is not evidence that ostarine is a proven, safe way for a healthy person to build muscle, lose fat or improve athletic performance.
