Question About Anti-Depressant Effectiveness?

I have had problems with obsessive thinking ever since I was little and in my junior year of college severe depression struck. I started getting this bizarre head pressure. about 7 years or more ago I started taking lexapro and buspirone, which took the head pressure away and made me feel better. I've also been seeing a therapist for the past year and practicing CBT, which has helped tremendously. However, I have maintained a lot of emotional numbness, and sexual side effects from the lexapro have always been there. So, I recently added Wellbutrin and I think after a few weeks it's starting to work. My question is this...

Today I've sort of freaked myself out b/c I came across several articles on the internet that have said antidepressants stop working after a while. The "poop out" effect as it's apparently termed. Does this happen to a majority of people, or is it rare? Does it only happen to certain kinds of people?

Please share if you have answers to these questions. Thank you.

Thanks for the response. I actually emailed two prominent doctors (who are both professors as well) who have conducted research on the issue and written articles about it. To my suprise, Both stated, in definitive terms, that the "poop out" effect happens to only a small percentage and is usually fixed by tweaking the medication. One of the physicians, who was more detailed in his response, stated that the medication could still be working but other problems are layered on top of it. His example was a car that encounters a steep incline--the motor still works fine, but the car will start struggling more b/c of the hill.

Hope this allays fears if anyone else was worried about this. And thanks for the response and the welcome, Karen. Everything seems to be working for me great so far, but regardless I'm glad to be a part of this forum and toss in my experiences with medication and therapy (CBT to be precise), which have all required work but produced positive results.