The 33-year-old was given a year-long suspension earlier this month after he tested positive for cocaine following a World Cup qualifier in October.
FIFA partially upheld his appeal against the sanction after the Appeal Committee of world football's governing body heard his case. His ban has been reduced to six months, meaning he will become eligible to play again in May next year.
In a statement, FIFA said: "The FIFA Appeal Committee after taking into account all the circumstances of the case, in particular the degree of fault of the player, considered a six-month period of ineligibility to be a proportionate sanction."
Guerrero tested positive for cocaine metabolite benzoylecgonine after a qualifier against Argentina on October 5 and was suspended for an initial 30-day period, which kept him out of his country's play-off victory over New Zealand.
His subsequent year-long ban was backdated to November 3, which initially meant he would not be available for the World Cup finals in Russia, which start next June.
Guerrero, who plays for Flamengo, scored five goals in qualifying to help his side secure fifth place in the CONMEBOL section.
Photo by: Getty Images. Caption: Peru captain Paolo Guerrero