It's drunk as a one-shot ritual at dawn on one specific date, August 1st, taken on an empty stomach to ward off bad luck for the coming year.
Caña con ruda is Paraguay's cane liquor (caña) infused for weeks with sprigs of ruda (rue), a bitter herb long used medicinally by the Guaraní. Each August 1st — observed across Paraguay and neighboring parts of Argentina as a day honoring the earth — people take a small shot of it before breakfast, sold and poured at kiosks and homes alike.