I did a Google search and a PubMed search. In the first one, I found some advertisements on many web sites and Chitosan is presented such as a miracolous new therapy against obesity. In the PubMed search, I found some studies which recommend Chitosan in addition (and not alone) to the patient's usual therapy and other studies which find Chitosan ineffective. 

The results on PubMed are not similar to the information that the patient reads on Google: they are based on scientific evidence, they are not advertisements. Sometimes, it is difficult to explain to the patient that his Google's search is not comparable to PubMed's search.