I asked Veli-Jukka Uitto, professor and head of oral microbiology at the University of Helsinki, Finland:

"We have a mouth rinse containing chlorhexidine gluconate that is safe and effective against most oral bacteria. It is however recommended to be used only occasionally under a doctor's or dentist's prescription. The reasons are: 1) It is killing both bad and good bugs. The good bacteria protect the mouth against the bad ones. 2) It often stains tongue and teeth brown. 3) It affects normal tasting 4) Some people are sensitive to it. 5) The rinsing solution does not reach under the gum lines. Therefore if there are deep gum pockets they have to be cleaned professionally. Other commercially available mouth rinse solutions are rather ineffective against oral bacteria, no matter what their ads claim."