The World Curling Federation (WCF) suspended Armstrong in February after he had tested positive for Tamoxifen.

Armstrong, 62, claimed that the banned drug had been prescribed for his late wife when she was receiving treatment for breast cancer and had got mixed up with his own medication.

He appealed against a the WCF decision and CAS held a hearing in Toronto in June, the results of which have just been announced.

The CAS ruled that the "WCF Panel did not properly exercise its discretion" in assessing the 18-month penalty, noting the accidental nature of the offence and the obvious lack of benefits to Armstrong from taking the drug.

"The sanction imposed on an athlete must not be disproportionate to the offence and must always reflect the extent of the athlete's guilt," the CAS report said.

"The fact that the Appellant stored his own medicine together with the medicine of his wife in a box and also reused containers of Tamoxifen, certainly does not constitute an exercise of utmost caution."

The six month ban ended on September 6 so Armstrong can begin competing again immediately, which will boost his hopes of qualifying to defend his title at Sochi in 2014.

"Absolutely, it's a relief," Armstrong told the Calgary Herald.

"Was there an adverse analytical finding? Yes.

"Could it be explained? Yes.

"And at the end of the day, that's what they decided.

Canada's Jim Armstrong celebrates winning the gold medal at Vancouver 2010

"It certainly doesn't negate the fact there was an offence.

"But there's an asterisk on it.

"They saw what it was an how it came about and applied a little bit of compassion to a very unwieldy circumstance.

"Under the circumstances, I think it's as close to vindication as I can get."

Details of the positive test came on the eve of the World Wheelchair Championships Chuncheon City, South Korea, in February and force Armstrong to return home to Canada without defending the title he had won at Prague the previous year.

In 2011 Armstrong was fined $30,000 (£19,000/€23,000) by an American court after selling counterfeit erectile dysfunction drugs.

The WCF said in a statement that they had "noted the decision of CAS to confirm the Anti-Doping Rule Violation of Mr Armstrong but to reduce the sanction imposed by the WCF's Independent Hearing Panel.

"The new sanction imposed on Mr Armstrong is six months meaning he can resume curling activities as from 6 September 2012."

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