or those with serious infections. apoquel may increase the chances of developing serious infections and may cause existing parasitic skin infestations or pre-existing cancers to worsen. new neoplasias were observed in clinical studies and post-approval. most common side effects are vomiting and diarrhea. feeling better? [dog] i'm speechless. [dog] thanks for the apoquel. that's what friends are for. ask your veterinarian for apoquel. next to you, apoquel is a dog's best friend.