The 31-year-old took the weight suppressant Phentermine after returning from a life-threatening fall in which she split her pancreas.
Payne, who rode at Royal Ascot last week, failed a drugs test at the 11 June Swan Hill Cup meeting in Victoria.
She is banned until 21 July following a Racing Victoria inquiry.
Payney is likely to return to Ascot for the Shergar Cup, racing's team event, on 12 August.
She pleaded guilty to taking Phentermine and said she took "full responsibility" for her actions, saying she was "disappointed and embarrassed".
"The onus is 100% with me as a rider to know what I am taking and the rules around it regardless of whether it has been prescribed to me or not," she said following Thursday's inquiry.
"Going forward, I'm very much looking forward to finding a solution in working with my surgeon."
Payne only returned to Australia after she rode Kaspersky into fifth place in the Queen Anne Stakes at Royal Ascot on 20 June.
Michelle Payne, the only female jockey to win the Melbourne Cup, has been banned for a month for taking a banned substance.