Heading off depressive illness evolution and progression to treatment resistance.

Viewing recurrent depression as a potentially progressive illness may help transform treatment toward earlier, more consistent intervention and prevention. Evidence indicates that recurrent stressors, episodes of depression, and bouts of substance abuse can each show sensitization (increased reactivity upon repetition) and cross-sensitization to the others, and drive illness progression and treatment resistance. These long-lasting increases in pathological responsivity appear to be mediated by epigenetic mechanisms involving alterations in chemical marks placed on DNA and histories. These types of sensitization effects are amenable to clinical attempts at amelioration and prevention, and provide treatment targets and strategies to minimize the likelihood of illness progression to treatment resistance.