Biles, 19, was forced to publicly address her ADHD and her approved use of the medication after the leak.
The documents were illegally obtained from a WADA database. They revealed that Biles tested positive for the medication, which the gymnast was given permission to use by the International Gymnastics Federation.
WADA condemned the attack, for which the alleged espionage group Fancy Bears claimed responsibility.
The gold medalist took to Twitter to address the situation and wrote, "I have ADHD and I have taken medicine for it since I was a kid. Please know, I believe in clean sport, have always followed the rules, and will continue to do so as fair play is critical to sport and is very important to me."
According to ABC News senior medical contributor Dr. Jen Ashton, medications like methylphenidate, which is widely known by the brand names Ritalin and Adderall, "are thought to work by enhancing neurotransmitter function in the brain."
She said such drugs would not give an athlete an edge.
"I think that athletes are so in tune with how their body feels during competition and how their mind focuses that to add anything that will alter that is not a risk most will take," said Ashton.
She added that WADA requires that ADHD be diagnosed by "experienced clinicians" and that methylphenidate be prescribed as a "medical best practice treatment."
Biles followed WADA's requirement to file for a therapeutic use exemption, which allows an athlete with a medical diagnosis to use a prohibited drug.
ADHD is commonly diagnosed during childhood and often lasts well into adulthood. At least 5 percent of children suffer from ADHD in the U.S., according to the American Psychiatric Association.
Final Five phenom Biles posted another tweet, letting her fans and supporters know that this incident will not knock her down. "Having ADHD, and taking medicine for it is nothing to be ashamed of nothing that I'm afraid to let people know," she wrote.