Ostarine: the performance-enhancing drug giving anti-doping agencies a headache

A drug designed to help cancer patients rebuild wasting muscles has become one of the most contentious substances in elite sport – and the scientist who discovered it now spends more time trying to stop people using it than encouraging its medical use.

James Dalton, who developed ostarine in the early 2000s, recently told the New York Times: “I spend more time now trying to stop people from using it than trying to get people to use it.” His frustration highlights a growing crisis in anti-doping, where even innocent athletes are testing positive for a drug that can be transferred through sweat or contaminated supplements.

Ostarine belongs to a class of drugs called selective androgen receptor modulators, or Sarms. Dalton and his team created these compounds as a safer alternative to traditional steroids for treating muscle wasting, osteoporosis, frailty and other conditions linked to ageing. Unlike steroids, which must be injected, Sarms can be taken as tablets or capsules, making them far easier to use.

The appeal was obvious. Traditional anabolic steroids do build muscle – the anabolic effect – but they also trigger unwanted male sexual characteristics. These include body hair growth, aggression, male pattern baldness, acne and breast tissue development in men. Women who abuse steroids can experience voice deepening and menstrual changes.

Sarms were meant to deliver only the muscle-building benefits without these side-effects. Ostarine, also known as enobosarm, showed particular promise for lung cancer patients losing muscle mass. More recently, researchers have investigated whether it could prevent muscle loss in people taking weight-loss drugs like Wegovy, where significant muscle is often lost alongside fat.

Despite this potential, no Sarm has passed the clinical trials needed for medical approval. There are concerns the drugs may cause liver damage, as reported in some users. Ostarine remains unapproved for human use more than two decades after Dalton’s initial research was published.

This hasn’t stopped it reaching athletes. When Dalton’s team published their work, the chemical structure became public knowledge. Black market manufacturers seized the opportunity, packaging ostarine as a sports supplement. Because selling Sarms as supplements is illegal, they’re often labelled “for research purposes” or “not for human consumption” – a transparent attempt to skirt regulations.

The World Anti-Doping Agency (Wada) recognised the abuse potential early, adding Sarms to its prohibited list in 2008. On the 2026 Wada prohibited list, ostarine appears under “S1.2 Other Anabolic Agents”, banned at all times in all sports.

Complicated and unfair

The problem has escalated dramatically. Over the past two years, ostarine has become the most commonly detected Sarm in Wada laboratories, appearing in 114 athlete samples. But here’s where things get complicated – and deeply unfair – for many athletes.

Sport operates under strict liability. Athletes are responsible for any banned substance found in their samples, regardless of how it got there. Even unintentional contamination can result in a ban.

The quality control of many supplements is poor, meaning products can contain traces of ostarine without declaring it on the label. The US Anti-Doping Agency maintains a list of high-risk supplements, with ostarine appearing undeclared in 19 products.

Athletes hoping to challenge a positive test must have kept the supplement and pay for independent testing – an expensive process with no guarantee of success. Sports authorities strongly recommend athletes only use supplements batch-tested by Informed Sport or NSF Certified for Sport – organisations that verify products are free from contamination.

Ostarine can also transfer between people. Athletes have successfully argued their positive tests resulted from sharing equipment. In one recent case, an athlete proved ostarine could transfer through a sweaty neoprene support shared with another athlete. Officials accepted the transfer explanation and dropped the charges.

Other cases have shown the drug can pass through bodily fluids like saliva.

This creates a profound dilemma for anti-doping authorities. Modern laboratory equipment is extraordinarily sensitive, capable of detecting minute quantities of drugs. But a urine test cannot distinguish between someone who deliberately took a large dose, someone who unknowingly consumed a contaminated supplement, or someone who absorbed traces through contact with another person’s sweat.

The burden of proof falls entirely on the athlete. They must explain why a banned substance is in their system, often at considerable personal expense. This same problem affects all Sarms, not just ostarine.

Dalton himself is now trying to solve the mess his discovery helped create. As co-chair of the Scientific Advisory Board of the Partnership for Clean Competition, he’s funding research into sports drug testing. The group’s priority is finding ways to differentiate between contamination and deliberate doping.

The hope is to identify marker compounds in urine that could definitively show whether a positive test resulted from intentional use or inadvertent contamination. Such a breakthrough would spare innocent athletes the ordeal of proving their innocence while still catching genuine cheaters.

Until then, a drug designed to help the sick continues to threaten the careers of athletes who may never have chosen to take it – and the scientist who created it remains caught in the middle, fighting against the unintended consequences of his own research.

Tom Bassindale does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.