The Athletics Integrity Unit (AIU) revealed that Kipyokei's sample, which was taken on October 11, 2021 after her victory, contained traces of triamcinolone acetonide.
The medical cream, commonly used to treat various kinds of skin conditions, contains a glucocorticoid that is banned at races unless an athlete has permission to use it.
Kipyokei has now been charged with using the product and tampering with the AIU's doping control and investigation, the AIU continued.
The Kenyan runner finished the 125th Boston Marathon win a time of 2:24:45.
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