Quinine
From Cookipedia
What is quinine?
Quinine is a natural white crystalline alkaloid having fever-reducing, antimalarial, painkilling, and anti-inflammatory properties and a bitter taste.
Quinine was the first effective treatment for malaria. It remained the antimalarial drug of choice until the 1940s.
Made from the bark of cinchona trees, the Peruvians would mix the ground up bark with sweetened water to offset the bark's bitter taste, thus producing tonic water.