Ukraine's women's quadruple sculls crew was stripped of its bronze medal on Thursday after one of the rowers failed a drugs test.
Olena Olefirenko, 27, tested positive for a stimulant and the team has been disqualified, said IOC spokeswoman Giselle Davies.
Australia will now take bronze behind Britain in silver and winners Germany.
Hungarian weightlifter Zoltan Kovacs has also been thrown out of the Games for refusing to take a drugs test.
On Wednesday, the International Olympic Committee insisted doping was "not ruining the Games".
Two Olympic champions - Hungary's discus gold medallist Robert Fazekas and Russia's women's shot winner Irina Korzhanenko - have already been stripped of their medals and eight athletes have now failed doping tests.
Three other competitors, including Greek sprinter Kostas Kenteris, dropped out following doping test violations.
"We should keep things in perspective. There are 10,500 athletes and there have been some wonderful successes," said IOC spokeswoman Giselle Davies.
Olefirenko was found to have taken ethamivan, a stimulant
contained in one of the medications declared by the athlete but
labelled under another name.
The Ukraine delegation said that the medications were given to
the athlete by the team doctor Ganna Gryshchenko.
"She had listed the product believing in good faith it
was something permitted and there was no way she could be
aware it contained a prohibited substance," said Denis
Oswald, president of the International Rowing Federation
and an IOC executive board member.
The IOC has urged the world
rowing federation and Ukraine's Olympic association to consider
action against the doctor.
Meanwhile, Kovacs is the 10th lifter to have been sanctioned for drugs-related offences at the Athens Games.
The 27-year-old Kovacs competed in the under 105kg division but did not finish the competition.