Olympic and world swimming champion Cesar Cielo has tested positive for the banned substance furosemide but escaped suspension, the Brazilian Aquatic Sports Confederation (CBDA) said on Friday.
Cielo, the world record holder in the 50 and 100 metres freestyle, and three other swimmers tested positive for the diuretic at the Brazilian national championships in May and had been warned, the CBDA added.
"There was no indication of blame or negligence," the CBDA said on its website, adding "(it is proven) there was no improvement in their performances."
The CBDA named the other three swimmers as Nicholas Santos, Henrique Barbosa and Vinicius Waked. The four had their results scratched.
Cielo, who won the gold medal in the 50 freestyle in Beijing, said in a statement that at a hearing of the CBDA he was able to prove a supplement he regularly took was contaminated.
"I've always used that supplement and never had a previous control shown a problem ... I think this was an isolated case," Cielo said.
"Throughout my career I've always been very careful with all medication I've taken. I consider myself an exemplary athlete in this respect," he added.
The 24-year-old won gold in the 50 and 100 freestyle at the 2009 Rome world championships and repeated the feat at the Dubai short course world championships last year.