All three failed out-of-competition tests before the opening ceremony, bringing to nine the number of doping cases in powerlifting.
All have been expelled from the Paralympic Village and banned from all international competition for four years.
The IPC identified the athletes as Uladzimir Buben of Belarus, Jabar T Jabir of Iraq and Olatumbosum Sulola of Nigeria.
Buben and Sulola showed accelerated levels of testosterone in their urine samples, while Jabir tested positive for Methyltestosterone.
IPC medical director Michael Riding said a new method of using carbon isotope ratio mass spectrometry had enabled the IPC Medical and Anti-Doping Commission to differentiate between testosterone produced in the body and that taken as a drug.
"It's serious, it's extremely disturbing and we're going to have to think how we're going to react to this terrible problem of drugs in powerlifting," Riding said.
The six other drug cheats revealed by the IPC president Robert Steadward and expelled from the Games and competition for four years were Hamed Abdul al-Jandal of Saudi Arabia and Anton Puskov of Bulgaria, who both tested positive to nandrolone, an anabolic steroid.
Masking agent
Last Saturday the IPC announced that Romania's Aurel Berbec had tested positive for the anabolic steroid stanozolol, Iran's Ali Mahmoudikordkheili (anabolic steroid methandienone), Bulgaria's Radko Radev (diuretic chlorthalidone) and Marina Diakonova of Russia (diuretic hydrochlorothiazide).
Of the nine powerlifting positives, seven were for steroids and two for diuretics, a masking agent.
All 159 out-of-competition tests had been completed while 500 tests were being conducted in competition, Riding said.
"It certainly appears to have had a shocking effect, as much on me as anyone else," he said.
Surprise
"I'm startled by this. It does show it was an effective strategy, on this occasion it took everybody by surprise."
Powerlifting officials have vowed to usher in more out-of-competition dope testing to cleanse the sport.
"More than 30 countries do out-of-competition doping controls," IPC powerlifting boss Pol Wautermartens said.
"However, this number will need to be increased in the future.
Unethical
"I tell athletes over and over again that doping is unethical and may do great harm to their health."
Wautermartens defended his sport's anti-doping record, saying it was the first in disabled sports to introduce controls more than 20 years ago.
No other sport has returned a positive doping test in Sydney, where out-of-competition testing was introduced for the first time.
These are the first Paralympians to fail doping tests since Barcelona in 1992.