Solo has accepted the warning and will still play for the United States in the Olympic tournament.
The 30-year-old Solo tested positive for Canrenone in a test on June 15.
"I took a medication prescribed by my personal doctor for pre-menstrual purposes that I did not know contained a diuretic," Solo said in a statement. "Once informed of this fact, I immediately cooperated with USADA and shared with them everything they needed to properly conclude that I made an honest mistake, and that the medication did not enhance my performance in any way."
Canrenone is classified as a specified substance, so its presence in an athlete's sample can result in a reduced sanction.
"As someone who believes in clean sport, I am glad to have worked with USADA to resolve this matter and I look forward to representing my country at the 2012 Olympic Games in London," she said.
A recent semifinalist on "Dancing With The Stars," Solo has been the regular U.S. keeper for nearly six years and backstopped the Americans to the 2008 gold medal in Beijing with some spectacular performances.
Considered one of the world's top keepers, she helped the Americans to a second-place finish in last year's World Cup, only a penalty kicks shootout loss to Japan denying Solo her first World Cup title.
She also is remembered for the contentious finish to the 2007 World Cup in China, when she helped the Americans reach the semifinals. But she was benched by coach Greg Ryan against Brazil for veteran Briana Scurry, a hero of the 1999 world champions. Scurry was rusty, the United States was routed 4-0, and Solo famously criticized Ryan's move.
"It was the wrong decision, and I think anybody that knows anything about the game knows that," Solo said. "There's no doubt in my mind I would have made those saves. ... You have to live in the present. And you can't live by big names. You can't live in the past."
Ryan dismissed Solo from the World Cup team. She wasn't allowed on the bench for the third-place game, did not participate in the medal ceremony and flew home from China on her own.
Pia Sundhage soon took over as coach and Solo has remained her top goalkeeper since.