The ban is effective from Dec. 1, 2016.
USADA said it had accepted Harper-Nelson's explanation that her positive test was caused by medication she was prescribed by a physician to treat hypertension.
"Harper-Nelson further explained that she made efforts to determine if the medication contained prohibited substances; however, due to using partial search terms, those efforts were unsuccessful," USADA said in a statement.
Harper-Nelson, who also clinched silver in the 100 metres hurdles at the 2012 London Games, said the medication had been prescribed after she was taken to hospital suffering from high blood pressure.
"As a result my physician prescribed a non-performance enhancing medication for high blood pressure that contained hydrochlorothiazide, water pill," she wrote on her Twitter page.
"I never hid my use of this required medication, but did fail to fully understand how its administration was governed by current doping protocols.
"I take full responsibility of my mistake and have fully cooperated with IAAF and USADA in the handling of the matter.
"I have learned a valuable lesson and hope my mistake will serve as a reminder to all athletes to be diligent in thoroughly checking any and all prescribed medications."
(Reporting by Kayon Raynor in Kingston; Editing by Greg Stutchbury)
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