It's true that overuse, meaning rinsing from 5 to 10 times per day, can cause a lot of problems. That's true with overusing anything. But what I found was pretty disgusting. Like most mouthwashes, Listerine has high levels of alcohol (around 26%), which is a desiccant or actually dries out tissue. This can cause your bad breath to worsen. Also, I read somewhere that Listerine can cause thrush, which is or like yeast infection in your mouth! Yuck!
Also, mouthwashes (not just overuse) can cause loss of taste and teeth staining. Wil and I noticed that, after we used Crest Pro-Health Rinse, which contains no alcohol, that our taste is altered or numbed. Now, I notice that effect when I use Listerine as well. Also, I read in a few places that Crest Pro-Health Rinse causes people's teeth to turn brown, especially in the gaps. See reviews on Amazon.com. So be forewarned! I am going to stop using Crest Pro-Health altogether and limit my use of Listerine to once a day. I am so freaked out!