Vomiting, Diarrhea, and lack of appetite. Allergic reactions to ragweed. Denamarin is well tolerated in most dogs, but it could trigger a few side effects such as diarrhea, vomiting, and inappetence.  If your dog is allergic to ragweed, Denamarin is likely to cause allergic reactions in your dog.  It is advised to look for any abnormality such as lack of appetite in your dog and report back to your vet about the observed effect of Denamarin.