The defining bitter alkaloid of cinchona bark, historically the world’s first antimalarial and still the reference bittering agent for tonic water and other carbonated drinks. Its sharp, clean bitterness at low doses gives tonic its unmistakable edge, while higher doses are toxic, so beverage regulations cap its concentration strictly. Derivatives remain in the antimalarial arsenal for resistant cases. Sourcing, extraction, and purity control ensure the food-grade material delivers consistent bitterness without unwanted cinchona alkaloids. Modern soft-drink makers use it at strictly regulated low levels.