London - Mo Farah repeatedly denied to the United States Anti-Doping Agency taking a legal supplement prior to the 2014 London Marathon, before changing his account once he learned the doctor who injected him had told the investigators he had taken it, the BBC reported on Monday.
The four-time Olympic champion had been asked by USADA whether he had been injected with L-carnitine, a naturally occurring amino acid, as part of its investigation into his former coach Alberto Salazar.
The supplement had been obtained through a contact of Salazar's in Switzerland.
As a result of the overall investigation, Salazar has been banned from athletics for four years over doping violations.
Two of Salazar's violations relate to using a banned method to administer an infusion of L-carnitine.
The US coach, who is appealing against his ban at the Court of Arbitration for Sport, led the Nike Oregon Project training group, where Farah was a star name from 2011-2017.
According to the BBC, Farah - who finished eighth in what was his first London Marathon in 2014 - was questioned by USADA officials investigating Salazar for nearly five hours a year after the injections took place.
in a transcript of the interview seen by the BBC, Farah repeatedly denied he had been injected.
"If someone said that you were taking L-carnitine injections, are they not telling the truth?" asked a USADA investigator.
Farah replied: "Definitely not telling the truth, 100 percent. I've never taken L-carnitine injections at all."
He is then asked: "Are you sure that Alberto Salazar hasn't recommended that you take L-carnitine injections?"
Farah responds: "No, I've never taken L-carnitine injections."
He is asked again: "You're absolutely sure that you didn't have a doctor put a butterfly needle... into your arm... and inject L-carnitine a few days before the London marathon?"
Farah says: "No. No chance."
He then left the room but returned soon afterwards with a different account, apparently after speaking with UK Athletics (UKA) head of distance running Barry Fudge.
Fudge had told USADA the previous day that Farah had been injected.
Farah then returned to the investigators and said: "So I just wanted to come clear, sorry guys, and I did take it at the time and I thought I didn't."
He is asked: "So you received L-carnitine... before the London marathon?"
Farah answers: "Yeah."
He adds: "There was a lot of talk before... and Alberto's always thinking about 'What's the best thing?' 'What's the best thing?'"
The USADA investigator then said: "A few days before the race... with... Alberto present and your doctor (Dr Robin Chakraverty, then UKA's chief medical officer) and Barry Fudge and you're telling us all about that now but you didn't remember any of that when I... kept asking you about this?"
Farah responds: "It all comes back for me, but at the time I didn't remember."
Farah - who will bid for a third 10,000 metres Olympic title later this year in Japan having abandoned his experiment to switch to the marathon - declined to comment to the BBC but his lawyers issued a letter.
"Interviews are not memory tests," they wrote.
"Mr Farah understood the question one way and as soon as he left the room he asked Mr Fudge and immediately returned ... to clarify and it is plain the investigators were comfortable with this explanation."
Fudge apparently did not disclose he had gone to Switzerland to collect the product.
Chakraverty said the decision to go ahead with the injection two days before the race had been a joint one with Fudge.
There is no evidence any rules were broken in the way the substance was administered.
Some research suggests that L-carnitine, if injected straight into the bloodstream, can help speed metabolism and boost athletic performance.