a category of interrelated mental illnesses involving anxiety reactions in response to stress. The types include: 1) generalized anxiety, by far the most prevalent condition, which strikes slightly more females than males, mostly in the 2035 age group; 2) panic disorder, in which a person suffers repeated panic attacks. Some 25 percent of Americans are subject to this ailment, about twice as many women as men; 3) obsessive-compulsive disorder, afflicting 23 percent of the U.S. population. About two-thirds of these patients go on to experience a major depressive episode; 4) posttraumatic stress disorder, most frequent among combat veterans or survivors of major physical trauma; and 5) the phobias (e.g., fear of snakes, crowds, confinement, heights, etc.), which on a minor scale affect about one in eight people in the U.S. Drugs that have proven effective against anxiety disorders are beta blockers, which act on adrenaline receptors; anxiolytics; antidepressants; and serotonergic drugs. Regular exercise has also proved beneficial.