The International Amateur Athletic Federation suspended Mitchell when he tested positive for testosterone last April, pending an appeal to the US Track and Field doping panel.
He was cleared last month, but the US panel did not make the reasons for its decision public.
Britain's Daily Telegraph claimed on Thursday that Mitchell escaped a ban by claiming the high level of testosterone in his sample was the result of having sex at least four times the night before and drinking five bottles of beer.
British team doctor Dr Pat Milroy told the newspaper: "Testosterone levels will rise after sex, but only to the body's normal limits."
Testosterone is a hormone which occurs naturally in the body, but can enhance performance by building muscle and reducing the recovery time after training.
IAAF media director Giorgio Reinieri said the case would not be studied by their own doping commission, which will then submit a report to a full IAAF council meeting in May.
He said the US panel made their decision on the basis that they were "not sure from where the testosterone came, if it was a product of the body itself or the result of something wrong".
Reinieri added: "That was the explanation sent. There are some special situations that can justify this high level of testosterone, according to the USATF panel."
Mitchell began running at the age of six and won bronze medals in the 100 metres at the 1991 World Championships and 1996 Olympic Games in Atlanta.
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