Military Rations Pills (兵糧丸, Hyōrōgan) are special pills that replenish one's chakra and nourish the body. It is made up of powerful stimulants and nutrients, said to allow the user to keep fighting for three days and three nights without rest. At the end of the three days effect, the shinobi is brought to the point of complete and utter exhaustion.
These pills are based on the actual world military rations pills used in Japan, mainly during the Sengoku period (mid-15th – early 17th century). They were made from rice, various flours, dried vegetables and fruits, seeds, and various other ingredients.
In the anime, Sakura Haruno created her own version of the Military Rations Pills. They are supposedly weaker than regular ones, as Sakura would deliver dozens of them to Naruto Uzumaki on a daily basis while he was training. They are also intended to have more medicinal purposes and be easier to consume. As a consequence, they taste awful, with Sai calling them "mud balls".