Abby Dahlkemper, a defender for reigning Women's World Cup champion United States, was issued a public warning Friday by the US Anti-Doping Agency for not obtaining a therapeutic-use exemption (TUE) for a banned medication.

The 24-year-old has played 18 matches for the American side, most recently last month against Mexico, and plays for the league-leading North Carolina Courage of the National Women's Soccer League.

Dahlkemper used the prescription medication spironolactone, a prohibited substance by the World Anti-Doping Agency, as a skin treatment under doctor supervision and declared so on her doping control form but had not obtained a TUE prior to being drug tested.

"As athletes, we are responsible for knowing about the medications we take," Dahlkemper said. "I made the mistake of not being more diligent about a medication my doctor prescribed for my persistent skin condition and I should have confirmed that the medication was free of all banned substances.

"The medication I am taking does not have any performance-enhancing effects and my use of this medication has since been approved by USADA," she said. "I appreciate US Soccer guiding me through this process and I'm grateful that this has been resolved."

Dahlkemper later obtained a TUE for the medication, missing an NWSL match last month while the paperwork was processed.

"She received the medication from a personal doctor to treat acne and it is not related to performance enhancement in any way," US Soccer said in a statement.

"Abby had declared the use of her medication on her doping control form at the time of the sample collection, and has subsequently obtained a TUE for the medication from USADA, so she can continue to take it."