COMFORTIS (Spinosad) may cause different adverse reactions depending on whether it is taken by your dog or your cat. Common adverse reactions in cats include: Anorexia, Ataxia, Decreased appetite, Diarrhea, Hypersalivation, Lethargy, Pruritus, Vomiting, Weight loss COMFORTIS for dogs may cause the following adverse effects: Anorexia, Ataxia, Cough, Decreased activity, Decreased appetite, Diarrhea, Excessive salivation, Hyperactivity, Hypersalivation, Incoordination, Increased appetite, Increased thirst, Itching, Lethargy, Pruritus, Redness of the skin, Seizures, Trembling, Vocalization, Vomiting, Weight loss