A report released Friday on the sudden death of Medina Spirit was unable to determine what killed the Kentucky Derby winner, though it found evidence of a possible heart attack. It found no banned substances.

Prior to the report’s release, two equine experts speculated that a blood doping drug known as EPO could have been to blame for the thoroughbred’s tragic demise.

EPO has become increasingly attractive to trainers because of the blood-boosting impact from injecting even small amounts of the drug – a technique called micro-dosing, and the difficulty in detecting the prohibited compound, experts told The Post.

The drug quickly disappears from a horse’s system — usually within a day or two — yet the benefit of increased stamina from more oxygen-rich blood can last for four or five weeks.  

Medina Spirit was just three years old when he collapsed and died of an apparent heart attack after a light workout at the Santa Anita track in California on Dec. 6. Yet the necropsy report, conducted by the California Animal Health and Food Safety lab at UC Davis, was inconclusive as to the cause of death.

The state agency overseeing the report noted that an ulcer medication and a diurectic were found in blood and urine samples and that the horse’s thyroxine levels were below normal. 

It also noted that Medina Spirit had an enlarged spleen, lungs that were swollen and foam in his windpipe — all typical in sudden horse deaths but also commonly seen in cardiac failure.

The necropsy found no evidence of any illicit drugs.

“No other drugs, heavy metals (including cobalt) or toxicants were detected,” the California Horse Racing Board said in a statement.

The director of the lab told The Post last week that EPO, a synthetic agent, would be looked into as a possible cause. 

“There’s certainly a lot of awareness about this issue,” Dr. Ashley Hill said in reference to EPO doping. “People do try to elevate red blood cell counts.” She added that there was a wide variety of potential causes of sudden death.

Blood doping could lead to “an increased risk of sudden death,” said Dr. Sheila Lyons, a specialist in equine sports medicine who has testified before Congress on how to stop the use of illicit drugs in the sport.

“That’s hematology 101,” added Lyons, who was not involved in Medina Spirit’s necropsy. “There’s a risk of a blood clot because the blood is so viscous. EPO does exactly the same thing to horses as it does to humans.”

A spokesman for the horse’s trainer, Bob Baffert, denied any EPO use.

“There is not even a scintilla of evidence, let alone a suggestion, that this horse received anything improper. It’s silly to suggest it,” Clark Brewster told The Post. “Medina Spirit, like all horses at this level of competition, was extensively tested pre-race and post-race. This idea of EPO blood doping is easily dispelled. It’s just nonsense.”

After Medina Spirit’s shock victory at the Kentucky Derby on May 1, the colt tested positive for betamethasone, a pain-killing, anti-inflammatory steroid that potentially can enhance a horse’s performance during a race. 

Baffert said a topical version of the drug was used to treat a rash on the horse’s hindquarters.  Kentucky racing rules allow the drug to be administered as long as it’s not in a horse’s bloodstream on race day. Any horse that gets an injection of betamethasone or other corticosteroid is prohibited from competing for 14 days.   

The late Medina Spirit could be disqualified at Churchill Downs because of the positive test, and Baffert has been banned from entering his horses on any of their racetracks for two years. New York racing officials also banned him.

Betamethasone was not mentioned in the necropsy. The drug doesn’t build up in the body like other forms of steroids and doesn’t have life-threatening effects, experts previously told The Post. 

Some believe that Medina Spirit, like other three-year-olds that race at elite levels, was simply too young, with a body not fully matured, to be thrust into competition, and his heart gave out.

But the experts had considered EPO as a potential cause because an athlete’s sudden death — whether it be man or beast — can result from blood doping, they said.  

It’s the the same drug linked to heart problems in humans and the cheating scandal involving Lance Armstrong and other cyclists. 

In 1990 Dutch cyclist Johannes Draaijer, a Tour de France competitor, died of a heart attack a few days after a race. No cause was found, but his wife said he’d become sick after taking EPO. Repeated doses can lead to life-threatening anemia. It also thickens the blood, leading to clots and a higher risk of heart attack and stroke in humans, experts said.

“There have been dozens of deaths in cycling going back 30 years, and it became clear that these elite cyclists were dropping dead when EPO use first became evident,” Lyons said.

Dr. Rick Sams, who has detected various forms of the performance-boosting agent in horses when he headed the LGC Sports Science lab in Kentucky in 2018, said there is widespread use of EPO in horse racing.

Medina Spirit died just six months after a Washington Post investigation showed Baffert’s horses had a higher rate of death than those of any other top trainer. Seven of the sudden deaths happened in the same stable in California between 2011 and 2013.

Baffert said he’d been injecting those horses with thyroxine, a hormone that can increase energy but is commonly prescribed to treat hypothyroidism.

Last month, he was in New York and on the hot seat when a lawyer for the New York Racing Association grilled him about Medina Spirit’s positive test for betamethasone and six other drug violations involving horses Baffert trained between 2019 and 2020.

The issue of EPO doping wasn’t raised at Baffert’s New York hearing, though its use has alarmed regulators for years.

“It is, I would say, just about epidemic use in our industry,” equine expert Dr. Mark Cheney told the Kentucky Equine Drug Research Council back in 2018.

He noted that there was an increase in horses getting a second wind at the finish line in their races — a sudden surge that could be attributed to EPO doping.

“Some trainers, I’m not going to mention any names, their horses are just rebreaking at the eighth pole.”