Difficulty concentrating is a normal and periodic occurrence for most people. Tiredness and emotional stress can cause concentration problems in most people. Hormonal changes, such as those experienced during menopause or pregnancy, can also affect how we think and concentrate. Concentration problems, when present to an excessive degree, are also characteristic of certain physical and psychological conditions. The hallmark condition associated with difficulty concentrating is attention-deficit hyperactivity disorder (ADHD), a condition that has been increasingly diagnosed in both children an adults in recent years. Rare conditions that affect the brain and some emotional problems as well as endocrinologic disturbances can also influence an individual's cognitive functions and thus impair concentration.