Despite the common misconception, a koala bear does not get a high from consuming eucalyptus leaves. People have speculated that koala bears sleep for so many hours because of intoxication from their diet consisting entirely of eucalyptus leaves.
Koala bears sleep for an average of over 20 hours a day. Koalas need this much sleep because of the amount of energy they expend digesting eucalyptus leaves. Digestion is so tiring because these leaves are high in fiber. However, the leaves are lacking in overall nutritional value and contain toxins. The only mammals that can tolerate the toxins contained in eucalyptus leaves are koalas and sugar gliders.