Former world 100 metres record holder Asafa Powell and Olympic 4x100 relay silver medallist Sherone Simpson have both tested positive for the stimulant oxilophrine at last month's Jamaican athletics championships.
In a statement on Sunday, Powell said he had tested positive for the stimulant, which has similar properties to ephedrine but a different chemical structure and is on the World Anti-Doping Agency's (WADA) banned list.
"I want to be clear in saying to my family, friends, and most of all my fans worldwide that I have never knowingly or wilfully taken any supplements or substances that break any rules. I am not now, nor have I ever been, a cheat," Powell said.
Powell, who has never won an individual global sprint title, held the 100 world record between 2005 and 2008 when his mark of 9.74 seconds was broken by current record holder and fellow-Jamaican Usain Bolt.
Simpson, who was a member of the Jamaican 4x100 metres relay team who won the silver medal at last year's London Olympics, said she had been notified that she had tested positive for the same drug at the trials.
The 28-year-old Jamaican finished equal second in the 100 metres at the 2008 Beijing Games and won a gold medal in the 4x100 relay in Athens four years earlier.
"This is a very difficult time for me," Simpson said in a statement.
"As an athlete, I know I am responsible for whatever that goes into my body. I would not intentionally take an illegal substance of any form into my system."
Earlier sources close to Jamaican athletics said five athletes, including two Olympic medallists, had tested positive for banned performance-enhancing drugs at the championships.
The sources said two of the athletes were sprinters while three competed in field events. They said one of the athletes was a junior.
The managers for Olympic 100 and 200 metres champion Bolt and world 100 metres champion Yohan Blake said their athletes were not involved. Blake did not compete at the championships because of injury while Bolt won the 100 metres.
Jamaican Anti-Doping Commission (JADCO) chairman Herb Elliott confirmed the body had received "reports of adverse analytical findings from "A" samples".
"The process of the result management has commenced in accordance with the JADCO Anti-doping rules," he told Reuters.
"We cannot disclose any further information until the athletes have responded to notification of the "A" sample."
Last month Jamaica's most successful female athlete Veronica Campbell-Brown tested positive for a diuretic, which can be used to mask the use of performance-enhancing drugs.
The twice Olympic 200 metres champion has been suspended by the Jamaican Athletics Administrative Association pending the outcome of a disciplinary panel hearing.