Two athletes have been sent home from Rio 2016 and Chinese swimmer Chen Xinyi has been provisionally banned after they failed drug tests.
Bulgarian steeplechaser Silvia Danekova has been thrown out of the Olympics after failing a drug test.
The 33-year-old tested positive for banned blood booster EPO and has been declared ineligible to compete in Rio by the Court of Arbitration for Sport (CAS).
Danekova, who raced in the heats of the 3000 metre steeplechase at London 2012, protested her innocence in an interview with Bulgarian television on Friday.
"I've been tested four times after entering the Olympic Village," she said. "[Results] of three of the samples were negative. It's an incredibly big shock.
"I don't feel guilty. I cannot tell you how humiliated I feel.
"I feel robbed emotionally. But we're coming from the east [Eastern Europe], we're too close to Russia..."
Further sanctions beyond the Games for Danekova will now fall under the jurisdiction of athletics' world governing body, the IAAF.
She joins Polish weightlifter Tomasz Zielinski in being sent home from Rio 2016, after CAS confirmed that a doping control had found evidence of Norandrosterone in his system.
Chinese swimmer Chen Xinyi, meanwhile, could become the third athlete to be thrown out after accepting a provisional suspension. That follows a positive test for hydrochlorothiazide.
The teenager finished fourth in the women's 100m butterfly final on Sunday, and subsequently pulled out of competing in the 50m freestyle earlier on Friday.
"The athlete accepted a provisional suspension on a voluntary basis; as a consequence, the athlete is provisionally suspended from competing at the Olympic Games Rio 2016," read a CAS statement.
"The procedure will continue and the CAS ADD [Anti-Doping Division] will issue a final award before the end of the Games."