Former Olympic champion Therese Johaug will miss the 2018 Winter Games after her ban in a steroid doping case was extended.

The Norwegian cross-country skier must serve an "appropriate" 18-month ban which expires next April, the Court of Arbitration for Sport said in announcing its appeal verdict on Tuesday.

"I am heart-broken. I had a dream to get to the Olympics," a tearful Johaug said at a news conference 25 minutes after the verdict was announced. "I think it is unfair, I feel I was unfairly treated."

Johaug asked CAS to overturn her initial 13-month ban — which cleared her to compete at the Pyeongchang Olympics next February in South Korea — while the International Ski Federation also appealed to seek a longer punishment.

The 2010 Olympics gold medallist and seven-time world champion tested positive for the anabolic agent clostebol during high-altitude off-season training last year.

'I feel I did everything right'

A Norwegian Olympic tribunal imposed just a 13-month ban after accepting she used a team-approved lotion in Italy to treat sunburned lips.

"I feel I did everything right," Johaug said in Italy at her training base. "I went to an expert who gave me this ointment and I asked him if the cream was on a doping list. The answer I got was no."

The three-member CAS judging panel did not agree that she was blameless.

"The [judging] panel noted that Ms. Johaug failed to conduct a basic check of the packaging, which not only listed a prohibited substance as an ingredient but also included [a] clear doping cautionary warning," the court said in a statement, noting her case was "inconsistent with her otherwise clean anti-doping record."

The ban stopped Johaug from defending her overall World Cup title last season, but would have cleared the 29-year-old star to return in November, three months ahead of the Pyeongchang Olympics.

Johaug won gold in the 4x5-kilometre relay at the 2010 Vancouver Games, and took individual silver and bronze medals in distance events at the 2014 Sochi Games.

13-month ban was 'on low end'

Skiing's world governing body argued that a 13-month ban was "on the low end of the range of reasonable sanctions."

FIS cited Johaug's failure "to read the doping warning label printed in red on the package," and her use of a medication she did not recognize that was bought away from her home country.

In a statement on Tuesday, the Switzerland-based ski body said it was "satisfied that an independent body had the opportunity to review all of the facts of this case and render an impartial verdict, which was the reason for FIS filing the appeal to CAS.

"This ensured that a fair and just decision for all parties could be determined in this case," FIS said.

Johaug's two medals in Sochi helped Norway place second in the medals table behind host Russia. Norway could top the standings when medals are reallocated after the International Olympic Committee finishes prosecuting cases of suspected systematic doping of the Russian team.