An association between behavioral and psychological changes and thyroid dysfunction has been recognized in humans since the 19th century. In a recent study, 66% of children with attention deficit-hyperactivity disorder (ADHD) were found to be hypothyroid, and supplementing with thyroxine was largely curative. Furthermore, an association has recently been established between aberrant behavior and thyroid dysfunction in the dog, and has also been noticed in cats with hyperthyroidism. Typical clinical signs include unprovoked aggression towards other animals and/or people, sudden onset of seizure disorder in adulthood, disorientation, moodiness, erratic temperament, periods of hyperactivity, hypoattentiveness, depression, fearfulness and phobias, anxiety, submissiveness, passivity, compulsiveness and irritability. After episodes, most animals appear to come out of a trance-like state and are unaware of their bizarre behavior.