The court said on Monday the ban had been extended six months and will be lifted in January, meaning the 34-year-old Flamengo man will miss the rest of this season, the World Cup and the first half of next season.
The 34-year-old had an initial one-year ban reduced to six months by Federation Internationale de Football Association and he returned to action for Brazilian club Flamengo earlier this month before being named in his country's provisional squad for their first World Cup since 1982.
Guerrero tested positive for Benzoylecgonine - which is a metabolite of cocaine - at a 2018 World Cup qualifying game against Argentina in October.
Peru captain Paolo Guerrero has been ruled out of the World Cup after a doping ban was increased from six months to 14 by the Court of Arbitration for Sport (CAS), Brazilian television network Globo said on its website on Monday.
Peru fans showed their support for him in Geneva.
Guerrero's appeal against the ban was upheld.
His lawyers argued the stimulant had not been performance enhancing, and was accidentally consumed in contaminated tea.
The Dutch-based union pointed out the CAS itself had accepted that Peru's all-time leading scorer did not intend to enhance performance and had not knowingly ingested the substance.
The ban, backdated to November, was reduced to six months less than two weeks later after the player protested to FIFA's appeal committee, meaning he was eligible for the World Cup.
CAS said that Guerrero bore "some fault or negligence, even if it was not significant, and that he could have taken some measures to prevent him from committing an anti-doping violation".
Guerrero scored his first goal on Sunday since the suspension, a header in Flamengo's 3-2 defeat at Chapecoense in the Brazilian championship.
"There is no reason for me to be suspended", he claimed after the match.
This is the second ruling by CAS that has a huge impact on Peru's 2018 World Cup journey. The three points helped Peru qualify for the playoffs- where they beat New Zealand to make it to Russia- at the expense of Chile.