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Ostarine held the promise of profound medical treatments. Something unexpected happened on the way to F.D.A. approval.

Credit...Illustrations by Zach Hackman

Feb. 2, 2026, 5:00 a.m. ET

Twenty-five years later, James Dalton proudly recalled “that euphoric moment” when the rats were dissected and he saw their prostate glands had shrunk.

“It still gives me goose bumps,” he said, pointing at his arm.

Dalton, 63, is a drug discovery scientist by trade with more than 100 patents under his name in the United States, and more than 500 internationally. This is a man who has dissected many, many rats.

But the specimens that day in early 2000 were special. Dalton, an associate professor at the University of Tennessee in Memphis at the time, was trying to develop a blockbuster medicine that would mimic the desirable effects of testosterone and anabolic steroids — including muscle growth and increased bone mass — while dialing down the unwanted ones.

Listen to this article with reporter commentary

His graduate assistant in the lab had stayed up all night harvesting the rats’ organs. Ordinarily, they would need to be weighed to determine any change, but in this case the results were unmistakable to the naked eye: The prostates treated with the researchers’ new drug had shrunk considerably, unlike those in the rats treated with testosterone. Everyone on Dalton’s research team gathered to gaze triumphantly.

The potential medical uses of this new drug were profound: building muscle mass in cancer patients with muscle-wasting conditions; improving strength in patients with osteoporosis; combating frailty in the elderly; treating incontinence in women with weak pelvic muscles.

“I knew we were onto something,” Dalton said with a widening smile.

Their study was published three years later. But something strange happened on the way to bringing the revolutionary medicine to market. Dalton got a call from the United States Anti-Doping Agency. There was a big problem. His drug was not approved for humans, but it was somehow turning up in Olympic-level athletes.

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Dalton’s laboratory creation, which would become known as ostarine, was causing havoc in the sports world. Decades later, it still is. It might have even prevented one American athlete from making the Olympic team for this month’s Winter Games in Italy.

In 2000, Dalton was a pioneering researcher in an emerging class of drugs known as SARMs, or selective androgen receptor modulators.

His research was aimed at treating significant medical problems. Testosterone and anabolic steroids, he explained, can provide meaningful health benefits — notably muscle growth — but come with side effects. For example, a woman being treated with testosterone could experience masculinizing issues like hair growth and a deepening voice. Dalton’s discovery offered patients the benefits without those unwanted effects.

The publication of Dalton’s team’s research in The Journal of Pharmacology and Experimental Therapeutics was like publishing a recipe on Epicurious. Patent be damned, pharmaceutical chefs around the world got to work cooking up the new drug. They knew there would be buyers.

Distributors in the United States, with names like Warrior Labz and Accelerated Genetix, purchased ostarine from abroad — manufacturers in China were especially productive — and sold it from sleek websites that boasted of tiptop quality control and “third-party testing for purity.” The distributors were often traced to residential addresses, or mailboxes at UPS stores in strip malls.

“We arrested a lot of these guys,” said Dan Burke, who was chief of cyber investigations for the Food and Drug Administration before joining the antidoping agency as its intelligence and investigations director. “These dudes have no idea what they’re handling.”

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Dalton began hearing from recreational athletes asking for guidance. The clinical trials with humans generally involved doses of 3-9 milligrams per day. Some weekend warriors were experimenting with 50-70 milligrams a day — or more. Dalton knew from his research that doses of 25 milligrams and higher on a daily basis could have unwelcome effects on males.

“It’s signaling in their brain, ‘OK, I’ve got enough testosterone,’ so that they stop producing testosterone,” he said. “Their testes shrink and they become infertile.”

The drug spread rampantly across the sports landscape. Soon, the U.S. Anti-Doping Agency was calling Dalton for information, and the World Anti-Doping Agency added ostarine to its list of banned substances. Weight lifters, runners, snowboarders, mixed martial arts fighters and motorcycle racers all tested positive. So did a cyclist, a pentathlete, a jiu-jitsu competitor and a hockey player.

“It seemed to come out of nowhere,” said Matt Fedoruk, the chief science officer for the U.S. Anti-Doping Agency. And suddenly it was everywhere.

The 2016 Olympic gold medalist in the pole vault tested positive for ostarine and was barred from the 2024 Paris Games.

A U.S. Olympic gold medalist sprinter was sanctioned for testing positive for ostarine — twice. A British sprinter tested positive at the 2020 Tokyo Olympics, resulting in his relay team being stripped of its silver medals.

There were horses, too. A trainer in New Mexico was given a 34-year suspension and a trainer in Canada was suspended for 20 years for giving their horses ostarine.

U.S. Customs and Border Protection seized thousands of pills at 11 ports of entry throughout the country over the past three years alone, according to a spokesman. Antidoping officials announced another sanction for ostarine on Jan. 23 — for a wheelchair rugby athlete.

In March 2024, Sydney Milani, an American bobsledder, returned to the United States after the World Cup tour in Europe and was preparing for a competition in Lake Placid, N.Y. She was on her way to the training room when she received an email from antidoping officials.

“I didn’t think it was for me,” she said. “Then I opened it and it had my name on it, and that’s when the panic set in.”

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**Ostarine was suddenly popular **because it worked well as a performance-enhancing drug. Athletes who used it generally got stronger. “Every clinical trial we did, if you take 3 milliliters once a day for 12 weeks, you’ll put on 3 pounds of lean muscle mass,” Dalton said.

The drug’s chemical properties also might have had a lot to do with the rash of positive doping tests.

Ostarine is described by chemists as a sticky substance, making it prone to latch on to other supplements through factory contamination. The protein powder you purchased at a supplements shop, for example, might contain some ostarine if the manufacturer wasn’t meticulous.

It is impossible to know which athletes intentionally used ostarine for performance enhancement and which accidentally consumed it through tainted supplements, but antidoping officials believe the latter group is sizable because positive doping tests often revealed only tiny amounts.

Another characteristic of ostarine is even more vexing and has caused an erosion of trust in the antidoping system: It is easily transmissible. Maybe too easily for existing antidoping rules.

One athlete who tested positive for ostarine was adamant that he had not taken it — but he recalled that he had shared a neoprene hamstring sleeve with someone who had. The athlete’s defense was cross-contamination through sweat.

“Is this even a plausible explanation?” Fedoruk recalled thinking when his research team at the U.S. Anti-Doping Agency was presented with the case.

After conducting an elaborate experiment involving the collection of sweat, Fedoruk concluded that yes, ostarine was secreted in perspiration and could be absorbed into a different athlete via a neoprene sleeve. The athlete, a world-class sprinter, was cleared of wrongdoing.

Milani had a similar case. But her experience left her wondering if the ostarine situation in sports is even more sinister.

Like many American bobsledders, she is a convert from track and field. Too few kids in the United States grow up dreaming of Olympic glory on a bobsled track, so the national team must draw from other sports that feature explosive speed and strength.

When her college track career ended at the University of Alabama, she was recruited to join the U.S. bobsled team. The pivot put Milani, who grew up on a farm in central Iowa, onto a mountainside ice chute — and into the stringent protocols of the U.S. Anti-Doping Agency and, globally, the World Anti-Doping Agency.

As a bobsled athlete with her eyes set on the 2026 Winter Games in Italy, Milani had a view of the less glamorous side of the American Olympic movement. U.S. national team members in many sports struggle to make ends meet financially. Milani said it was not uncommon for some teammates to sleep in their cars outside the training center.

On top of the financial stress is an antidoping program that bedevils athletes, even the clean ones who want a level playing field. Two aspects of the system, in particular, are chronic sources of complaints: whereabouts and thresholds.

Whereabouts rules, designed to prevent cheaters from eluding drug testers, require an athlete to constantly update a schedule, three months in advance, that shares daily overnight locations, a daily 60-minute time slot with a guaranteed location, and training, competition and other activity plans, including for school and work. Three whereabouts missteps trigger a doping sanction.

If you relish spontaneity, don’t become an Olympic athlete.

“It’s what drives a lot of athletes to retire,” Milani said about the whereabouts demands.

The thresholds issue raises grave ethical questions.

For athletes under the World Anti-Doping Agency code, there is no threshold, or permissible amount allowed in the body, for most banned substances, including ostarine. Zero tolerance. The argument is that even a trace amount could indicate that the athlete used the drug to enhance performance at an earlier time.

But what if contamination from something innocent is possible? Say, a hamstring sleeve? Or even sex?

The email Milani received from American antidoping officials said she had tested positive for ostarine at a level of 0.02 nanograms per milliliter, or roughly the equivalent of one drop of water in an Olympic-size pool. (The laboratories that conduct sports doping tests are equipped with instruments that can detect substances at the level of a picogram — one-trillionth of a gram.)

The antidoping officials explained that if Milani didn’t prove her innocence, she faced a four-year ban.

Milani adamantly denied using ostarine. Antidoping investigators learned that her boyfriend at the time, with whom she was living, was using ostarine and, unbeknown to Milani, had put it in an energy drink he made for himself but that she happened to share. She may have inadvertently ingested the drug that way. “The low level of ostarine detected in Milani’s urine samples was consistent with this one-time exposure scenario,” the U.S. Anti-Doping Agency said in a statement.

“All of us, we’re scared,” Milani said about the national bobsled team. “It’s terrifying that they don’t have thresholds for everything.”

The head of the antidoping agency acknowledged that the rule is problematic and some athletes are being unfairly punished.

“The science is really good now, which is why we’ve been advocating for fairer WADA rules to make sure athletes aren’t convicted for innocent and non-performance-enhancing exposure to prohibited substances,” Travis Tygart, the agency’s chief executive officer, said in an email.

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There is another exposure scenario that more forcefully challenges the zero-tolerance policy. Researchers have determined that ostarine can be transmitted through semen.

A few weeks before I spoke with Milani, a Swiss triathlete was exonerated after antidoping officials determined that “inadvertent contamination through intimate contact with her partner” had caused her positive test — for ligandrol, a pharmacological sibling of ostarine.

Antidoping officials, acknowledging that Milani had not intentionally used ostarine, reduced her penalty to a one-year suspension, beginning in March 2024. She had thought she would be in the mix for a spot on the team that will compete at this month’s Olympics, but missing such a critical period of training was a heavy blow to those hopes.

She now has her sights set on the next Winter Olympics, in 2030. But she is disillusioned with the antidoping system. She wonders what the real source was of the trace amount of ostarine in her body.

“I still think I got popped because of sex,” Milani told me. “When you think about that, as a woman, it’s clearly unfair.”

Several years after their breakthrough in 2000, Dalton joined his former collaborator Mitchell Steiner at a drug development company in Memphis. They licensed the new drug from the University of Tennessee, continued to tweak the formula and began clinical trials in hopes of eventually gaining F.D.A. approval. They never got it.

Ostarine still hasn’t been approved for use in humans, though Steiner continues to develop the drug, under the name enobosarm. His new company, Veru, has combined it with Wegovy to offset the muscle-wasting side effects common for GLP-1 weight-loss drugs. A late-stage clinical study has so far demonstrated that the drug is an effective treatment to maintain lean body mass in obese patients at a 3 milligram daily dose. Steiner hopes to submit an application for F.D.A. approval in 2029 or 2030.

Milani spent her year away from the national bobsled team back at the University of Alabama, training with her college strength coaches and building a nonprofit to raise money for U.S. athletes in need. Steps away in the provost’s office at Alabama at the time: Dalton, the developer of the drug that caused her banishment. He had pivoted his career into administration.

Dalton is no longer actively involved in ostarine’s development. Resigned to the reality that the drug is everywhere in sports, he now works to combat its use by athletes. He has advised the U.S. Anti-Doping Agency on ostarine cases and is chair of a scientific advisory board for a group that reviews and funds grants for antidoping research.

“I spend more time now trying to stop people from using it than trying to get people to use it,” Dalton said. “That wasn’t what I ever set out to do with this.”

He’s not part of the antidoping apparatus that will operate 24 hours a day during the Olympics this month in Italy. But he’ll be watching from home. His favorite sport at the Winter Games?

“Well, I’ve always loved bobsled,” he said.

Alain Delaquérière contributed research.

Audio produced by Jack D’Isidoro.

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