Thipe and Rapula Sefanyetso, who has also tested positive, are the latest among 10 South African athletes who have failed tests for banned substances this season.

Thipe tested positive at the African Athletics Championships in Benin in June and Sefanyetso, a promising men's 200m specialist, tested positive at the Yellow Pages Meeting in Pretoria in April.

"I don't know what is going on, but doping by South African athletes is becoming a serious problem," ASA President James Evans said.

"To have 10 athletes testing positive in a season is just not acceptable.

"South Africa seems to have some of the dumbest athletes.

"They know they will be caught, but they keep on using banned substances and making the same mistakes over and over again."

Thipe won the women's 100m and 400m events at the 2009 South African championships in Stellenbosch.

She then took time off for the birth of her first child, but made a comeback this season, setting the fastest times by a South African woman this year in the 100m (11.49 seconds), 200m (22.89) and 400m (51.52).

Comrades Marathon winner Ludwick Mamabolo is one of the 10 South African athletes caught doping

Of the 10 South African athletes to have tested positive this season, five are senior track and field competitors, two are juniors and three are road runners.

Evans said athletes were taking supplements and substances without understanding what they contained.

"During the International Associations of Athletics Federation (IAAF) World Junior Athletics Championship in Barcelona (in July), we had a discussion with the athletes," he said.

"We advised them not to use any substances.

"If they have to buy any medication, they should first get an expert opinion.

"The next moment, one of the junior athletes is off to a pharmacy to buy some nose spray.

"The pharmacist does not understand her and sells her something containing a banned substance, that is just stupid."

Among the athletes who have failed doping tests this season are Comrades Marathon winner Ludwick Mamabolo, who is facing a hearing after testing positive for methylhexaneamine, and former world junior long-jump champion Luvo Manyonga, who tested positive for methamphetamine, commonly known as "tik".

South African-born Turkish long jumper Karin Mey Melis was withdrawn from the London 2012 Olympics after the authorities learned she had earlier tested positive in a doping test.

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