During the hostilities between Spain and France from 1808 to 1813, Spanish physicians on the front lines of battle made a discovery that was tantamount to unveiling a secret military weapon. They developed a bitter green drink made from ground olive leaves, and administered it as a therapeutic beverage to wounded soldiers suffering from high fevers.
This drink brought down the patients dangerously elevated temperatures from above 104 F to a harmless low-grade level below 101 F. Thus, even feverish Spanish soldiers were able to quickly advance to the fighting ranks once again and push back their French counterparts.
Observing these renewed attacks, by 1811 the French medical corps sent out undercover agents. The military doctors wanted to learn what was happening among the Spaniards. Uncovering the medical secret, the French officer-surgeons quickly adapted the same pulverized green olive leaf drink as part of their own febrifuge (fever-lowering) remedy. The beverage worked so effectively that they prescribed the olive leaf concentrate as a substitute for cinchona bark, which had previously been their standard febrifuge.
From the book
Olive Leaf Extract
DR. Morton Walker