United States sports officials have been quick to defend the athletes whose medical information was publicly released by computer hackers this week. The documents showed that some top American athletes have exemptions to use drugs that are otherwise banned — exemptions that they requested and that were granted by antidoping officials.

While the hacked documents lay bare urine-test results, specific substances and the period of time they were taken, they do not reveal which doctors originally prescribed the drugs in question.

In at least one case — perhaps the most complicated exemption of those made public this week, that of tennis player Bethanie Mattek-Sands — the person behind the prescription is a former bodybuilder who does not shy away from discussing the use of prohibited substances.

That person, Dr. Eric Serrano, who has said that he has worked with “thousands of steroid-using athletes,” prescribed drugs for Ms. Mattek-Sands, who won the women’s doubles title at the United States Open on Sunday and a gold medal in mixed doubles at the Rio Olympics.