disorder and may be seen as a severi ty marker of the comorbid illness. 
Reported lifetime rates of comorbidity between major depressive disorder and panic
disorder vary widely, ranging from 10% to 65%  in individuals with panic disorder. In ap-
proximately one-third of indivi duals with both disorders, the depression precedes the on-
set of panic disorder. In the remaining two-th irds, depression occurs coincident with or
following the onset of panic disorder. A subset of individuals with panic disorder develop
a substance-related disorder, wh ich for some represents an a ttempt to treat their anxiety