( CNN ) -- Olympic gold medalist Sherone Simpson of Jamaica plans to file an appeal with the Court of Arbitration for Sport ( CAS ) after receiving an 18-month doping suspension Tuesday , with her agent calling the ban `` incredibly unjust . '' Simpson , who won gold at the 2004 Olympics in the 4x100-meter relay , silver in the 100 meters at the 2008 Games and silver in the 4x100-meter relay at the 2012 Olympics , tested positive for the banned stimulant oxilofrine at last year 's Jamaican national championships . The 29-year-old revealed last year -- on the same day former 100-meter world-record holder Asafa Powell of Jamaica and former world champion Tyson Gay of the U.S. said they had tested positive for banned substances -- that she would never `` intentionally take an illegal substance of any form '' but Jamaica 's anti-doping disciplinary panel Tuesday claimed she was `` negligent , '' The Jamaican Gleaner newspaper reported . The ban is backdated to last June , which means Simpson would be able to return to competition this December . `` The panel has given no written explanation as to how or why they came to this decision , '' Simpson 's agent , Paul Doyle , said in a statement sent to CNN . `` We feel that this ruling is incredibly unjust and we will be appealing to the Court of Arbitration ( for ) Sport immediately . '' Doyle added that the case for CAS should be `` very straightforward . '' `` Sherone took a legal supplement that was contaminated with oxilofrine , '' said Doyle . `` Two different labs that we commissioned to test the supplement both determined that oxilofrine was present and that it was not declared on the label . `` Additionally , on our advisement ( the U.S. Anti-Doping Agency ) ordered the supplement directly from the company and tested it themselves and confirmed the same . Subsequently , USADA has posted a warning on their website warning athletes not to take the supplement because it contains banned substances that are not declared on the label . `` These are the core facts of Sherone 's case and can not be disputed . Typically in such a case , the athlete is given a punishment ranging from a public warning to three months of ineligibility . The fact that the panel has given 18 months suspension and have provided no explanation as to why is unacceptable in our opinion . '' It was a double blow Tuesday for Jamaican athletes , since discus thrower Allison Randall received a two-year doping suspension , The Gleaner said . Powell , who also tested positive for oxilofrine , is expected to learn his fate Thursday . Simpson and Powell share the same physical trainer , according to The Gleaner . Simpson will be hoping for the same ruling handed out by CAS in February in the case of decorated Jamaican sprinter Veronica Campbell-Brown . Campbell-Brown , who has won more than a dozen Olympic and world championship medals , had her two-year ban for testing positive for a banned diuretic last May overturned .
Olympic sprint gold medalist Sherone Simpson is to appeal her doping suspension . Simpson 's agent Paul Doyle calls the 18-month ban ` ` incredibly unjust '' Simpson tested positive for banned stimulant oxilofrine at last year 's Jamaican trials . A ruling in the favour of fellow Jamaican athlete Ashley Powell is expected on Monday .