Shayna Jack is on the verge of returning to competitive swimming after serving her two-year drugs ban.

Jack has entered five events at the Queensland state championships in Brisbane which start on Saturday.

Jack's first competitive swim will be on Monday in a heat of the 100m freestyle.

The 23-year-old has also entered the 50m freestyle, 50m backstroke, 1500m freestyle and 50m butterfly.

Jack was initially banned for four years after testing positive to Ligandrol on June 26, 2019, almost three weeks before the world championships in South Korea.

The Queenslander appealed her ban to the Court of Arbitration for Sport (CAS) which reduced her suspension to two years, finding Jack did not knowingly ingest the substance.

Sport Integrity Australia (SIA) appealed that reduction, citing a need for clarity regarding anti-doping legal principles.

CAS rejected the SIA appeal last September, allowing Jack to return to the sport.

"I am now free to do what I love with no restrictions and am so overwhelmed with joy," Jack posted on Instagram in September after the CAS ruling.

"The nightmare is finally over."

CAS, in its full decision published in November last year, noted Jack admitted she didn't know how the substance was in her system but suggested three possible sources for her positive test.

Jack suggested supplements she took was could have been contaminated at manufacturing.

Another possibility was the supplements were contaminated by being prepared or mixed in a blender that may have been contaminated or contained Ligandrol.

A third possibility was Jack may have come into contact with the Ligandrol or ingested it as a result of using a pool and/or gym open to the public in Townsville or Cairns while training before the 2019 world championships.