David said: Meadowsweet has aspirin-like activity so it acts as a febrifuge reducing temperature. What you are asking about is called fever management. When the person is hot and feverish, using a diaphoretic like Yarrow, Boneset, Saffron, Elderflower, etc will increase temperature, then cause sweating and this lowers the fever. When someone has a high temperature and feels chills, this signals the body want to raise the temperature even more, but at that point the fever may be too high, so you use a febrifuge (or antipyretic) to bring the temperature down. In most cases fevers are useful , increasing immune response and elimination of metabolic wastes, but there is too much af a good thing.