1216 GMT December 06, 2019
The 30-year-old tested positive for an anabolic agent in three out-of-competition urine samples in November and December last year, BBC Sport reported.
He was found to have had testosterone pellets inserted in his body, the US Anti-Doping Agency (USADA) said.
"My doctor assured me that the United States Olympic Committee had approved the treatment," said Dwyer.
"Regardless of the result of the arbitration ruling, I have decided to retire from swimming to pursue other professional interests.
Dwyer said he was following a doctor-prescribed medical treatment that he did not realize contained the banned substance testosterone and noted that the panel said in its report that he was not significantly at fault for the violation.
He was part of the US 4x200m freestyle teams that won gold at the 2012 and 2016 Olympics. He also claimed bronze in the individual 200m freestyle at Rio Games in 2016.
USADA chief executive Travis Tygart said, "As noted in the panel's decision, USADA is independent of sport and here to help athletes ensure they compete clean and protect their health and wellbeing within the rules.
"It's frustrating that Mr. Dwyer did not take advantage of this support and hopefully this case will convince others to do so in order to protect fair and healthy competition for all athletes."