If any of the following serious side effects occur, stop giving Percorten-V and seek emergency veterinary medical attention; an allergic reaction (difficulty breathing; swelling of the lips, tongue or face; hives), increased blood pressure or sudden weight gain. Other less serious side effects may occur. Continue giving Percorten-V and talk to your veterinarian if your pet experiences insomnia, nausea, vomiting or stomach upset, fatigue, muscle weakness or joint pain, problems with diabetes control or increased hunger or thirst. Other side effects that occur rarely, usually with high doses of Percorten-V include thinning of the skin, cataracts, glaucoma, behavior changes. Other side effects may also occur. Talk to your veterinarian about any side effect that seems unusual or bothersome to your pet.