Zeng provided evidence to a USADA investigation that the prohibited substance was from an altitude sickness medication, which was prescribed to her parent and given to her in response to an illness.
USADA said the 19-year-old believed she was being given ibuprofen and therefore did not have to apply for a Therapeutic Use Exemption, which is required to authorise the use of a prohibited substance in sport.
Along with her five gold medals from the 2015 Toronto Pan Am Games, Zeng also dominated the Pan American Championships staged in Lima, Peru in September, sweeping six gold medals, including the all-around title.
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Zeng's ban began on Oct. 18, the date her positive sample was collected.
(Reporting by Steve Keating in Toronto Editing by Toby Davis)
