Simpson was the second Jamaican athlete to be handed a doping ban on Tuesday as Olympic discus thrower Allison Randall was suspended for two years after she too failed a drugs test during the 2013 national trials.
"Miss Simpson has admitted the anti-doping violation and ... now having listened and reviewed all the evidence and listened to the detailed submissions of councils, this panel is unanimously of the view that Ms Simpson was negligent in all the circumstances as an elite athlete and as such, the period of ineligibility will be 18 months," Lennox Gayle, a member of the Jamaica Anti-doping Disciplinary panel, said.
During a hearing in January, Simpson said a supplement provided by her Canadian trainer was responsible for her positive test.
Simpson's agent Paul Doyle said on Tuesday she would lodge an appeal against the ban.
"We feel that this ruling is incredibly unjust and we will be appealing to the Court of Arbitration of Sport immediately," Doyle said in a statement.
"The case in our opinion should be very straight forward. Sherone took a legal supplement that was contaminated with oxilofrine.
"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."
Simpson, the 2004 Olympic 4x100 relay gold medallist, said she was not familiar with one of the five supplements given to her but when she searched online, she noted that none of the substances printed on the bottle of Epiphany D1 appeared on the World Anti-Doping Agency's banned list.
"On our advice, USADA (United States Anti-Doping Agency)ordered the supplement directly from the company and tested it themselves and confirmed the same," said Doyle.
"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 cannot be disputed.
"The fact that the panel has given 18 months suspension and have provided no explanation as to why is unacceptable in our opinion. As a result, we will be seeking justice instead from the Court of Arbitration of Sport."
Simpson was one of five Jamaicans to test positive at last June's national championships. Both she and former world 100 record holder Asafa Powell returned adverse findings for oxilofrine.
Powell will hear his verdict on Thursday.
Randall, 26, who holds the Jamaican discus record with a distance of 61.21 metres, tested positive for the banned diuretic hydro-chlorothiazide - which reduces blood volume.
"The sanction imposed by the disciplinary panel is two years," Kent Pantry, another anti-doping disciplinary panel member, said.
Simpson and Randall's bans have been backdated to June 21 2013 - when they provided the samples.
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