Guerrero initially received a 12 month ban, which has now been reduced to six months on appeal, meaning the striker will be available for Peru's trip to Russia.
The South American nation will face France, Denmark and Australia in the Group stage.
"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," a FIFA statement read.
"The player tested positive for the metabolite benzoylecgonine, a substance included in WADA’s 2017 Prohibited List under the class “S6. Stimulants”, following a doping control test conducted after the match of the preliminary competition of the 2018 FIFA World Cup Russia played in Buenos Aires, Argentina, on 5 October 2017.
