The Switzerland-based body cut the bans to six months – a suspension already served by both runners – following hearings in New York last week. (Agencies)
"The CAS decided to reduce their period of ineligibility to six months, which has been already served. The athletes were already free to compete since June 18, 2014 after the CAS had granted a stay of the decisions of JADCO April 8 and 10, 2014," the body said in a statement.
"They put forward that the offense committed was minor because it was caused by contamination of the food supplement 'Epiphany D1' by the banned substance Oxilofrine and requested that the suspensions be reduced to three months,” the statement added.
A report in Jamaica Observer quoting Powell's publicist Tara Playfair-Scott said the CAS has ordered the Jamaica Anti-doping Commission (JADCO) to pay all costs involved in the Powell and Simpson hearing.
"CAS has not just reduced the sentences of both athletes but it also awarded all costs associated with arbitration for the CAS hearing as well as additional monies in legal fees to be paid by JADCO. It is believed to be one of the largest awards in the history of CAS," a release on Monday from Playfair-Scott said.
Powell and Simpson can now continue their lucrative careers on the international circuit and neither has wasted any time, and confirmed their participation at Tuesday's Luzern Spitzenleichtathletik in Lucerne, Switzerland.
"I never felt that I should not have received a sanction," Powell said in a statement.
"However, I always felt that the 18 months was not in line with a first time positive test result and it being proven it came from a tainted supplement,” he added.
Simpson said she was thankful for the outcome.
"I feel total relief and that we have finally been vindicated," the 29-year-old said.
"We both knew that we had done all we could to ensure the supplement was ok before taking it and our actions were not intentional and CAS has recognised that. I am truly thankful,” she added.
Powell and Simpson were banned in April by the JADCO after testing positive for the banned substance Oxilofrine at the National Championships last year.
In handing down the judgment, JADCO said Powell had been "negligent" and "at fault", and said Simpson was "negligent in all the circumstances".
Both athletes described the sentences - which would have sidelined them until December - as excessive and vowed to appeal, and their lawyer Paul Greene said on Monday the situation was one which could have been avoided.
"The real shame of this is that we can't go back in time to Dec 22, 2013 when they should have been back competing," he said in a statement.
"Had the JADCO followed the IAAF rules Asafa and Sherone would have had a hearing within three months and been able to compete all of 2014,” he added.
The nearly historic cost that JADCO will be required to pay is a sign from the CAS that JADCO's failures in handling their cases are unacceptable."
The Switzerland-based body cut the bans to six months – a suspension already served by both runners – following hearings in New York last week.