Proin ER may mask signs of incontinence due to urinary tract infection. Proin ER is not effective in dogs with incontinence due to neurologic disease or malformations. Proin ER may cause hypertension; therefore, use with caution in dogs with pre-existing heart disease, hypertension, liver disease, kidney insufficiency, diabetes, glaucoma, and conditions with a predilection for hypertension. Use with caution in dogs receiving sympathomimetic drugs, tricyclic antidepressants, or monoamine oxidase inhibitors as increased toxicity may result. Use with caution in dogs administered halogenated gaseous anesthetics as this may increase the risk of cardiac arrhythmias. A laboratory study on human blood revealed that phenylpropanolamine (PPA) used in conjunction with aspirin may potentiate decreased platelet aggregation. Proin ER may cause increased thirst; therefore, provide dogs with ample fresh water. The safe use of Proin ER has not been evaluated in dogs that are intended for breeding, or that are pregnant or lactating.