A study was designed to determine the safety of a drinking water additive that reduces plaque and calculus in dogs, and contains xylitol as an active ingredient. The randomized, double-blind, placebo-controlled study was performed in 15 crossbred dogs that were randomly divided into three groups and had their drinking water treated for 14 days with either: i) a commercial health care product (BreathaLyser Plus) at the recommended dosage, ii) an experimental health care product (BreathaLyser Plus containing five times the amount of xylitol), or iii) a placebo of purified water with a colour additive. Results demonstrated that the continuous administration of a commercial, drinking water, oral health product containing xylitol, at one and five times the normal inclusion rate, does not cause hypoglycemia or alter liver function in dogs.