Regarding my interest and enthusiasm for Targacept ( TRGT) and its "add-on" anti-depressant drug TC-5214, @lomu_j tweets, "@adamfeuerstein MDD market is being flooded with generics. Does '5214 have a chance?" MDD is the acronym for major depressive disorder and yes, the market is filled with cheap generics, but that hasn't crimped growth for branded antidepressants. Sales of branded antidepression drugs in the U.S. grew 18% to $12.5 billion last year, according to Bloomberg. The overall depression-drug market in the U.S. was estimated at around $16 billion, according to several analyst reports. Certainly as more generic drugs enter, the market size will decrease, but '5214 is intended initially as an add-on therapy, which means doctors will prescribe '5214 in combination with currently approved antidepressants. It's estimated that approximately 60% of patients treated for depression do not respond to first-line therapy, making them ideal candidates for add-on (or augmentation) treatment with '5214.