Super-featherweight world champion Alycia Baumgartner has returned an “adverse analytical finding” following a drug test, Matchroom Boxing says.
But the American, 29, has denied taking any illegal substances, declaring the test result “essentially impossible”.
The test was taken three days before Baumgartner defeated Greece’s Christina Linardatou in Detroit on 15 July.
In a statement, Matchroom said it is “committed to promoting a clean and fair sport for all athletes”.
On Instagram, Baumgardner wrote she had “no intention of sitting back in silence and letting this ‘play out.'”
The fighter said she had given three samples – one on 16 June, one on 12 July, and another on 15 July after her win over Linardatou.
It was the 12 July test – the middle one of the three – that was reported as ‘adverse’ to Matchroom on 12 August.
The results of that sample found mesterolone and methenolone acetate metabolites – two substances Baumgardner said she had “never heard of or used in any way”.
“To be abundantly clear, I know that I never have, never would, and never will take this or any other drug,” she wrote.
“Not only would doing so be unethical, but it would also be completely contrary to how I’ve trained my entire career.”
Baumgardner said that her other two tests – including the later one, provided on 15 July – were “clean and negative”.
Matchroom said it would assist Baumgardner and her team during this time, “affording her the appropriate due process”.
The statement added: “Matchroom was first informed of this result on 12 August.
“The applicable regulatory authorities are also aware and we defer to such bodies for further action and guidance as a full investigation is conducted.
“As we wait to receive further information, Matchroom will not be making any further comment.”
Baumgardner said she was “proud to be a role model for young girls”, the responsibilities of which she takes “very seriously”.
She added: “I plan to keep you all updated every step of the way as I work to ensure my reputation as a clean athlete remains fully intact.”
Baumgardner holds all the titles – WBA, WBC, IBF, WBO and The Ring – in the super-featherweight category.
She took her record to 15 wins from 16 fights when she beat Linardatou on points by unanimous decision.
The Ohio-born boxer hinted in her post-fight interview with Linardatou she would be willing to step up a weight division – from super-featherweight at 9st 4lb (59kg) to lightweight at 9st 9lb (61.4kg) – to take on the Republic of Ireland’s Katie Taylor.
It is the second anti-doping controversy to hit boxing in two weeks after Dillian Whyte’s “adverse finding” led to the cancellation of his bout against Anthony Joshua last Saturday.
