Side effects of phenoxybenzamine in cats include gastrointestinal upset (nausea, vomiting), weakness due to low blood pressure (hypotension), high blood pressure (rebound hypertension), abnormally small pupils of the eyes (miosis), increased eye (intraocular) pressure, fast heart rate, sinus congestion, and loss of balance (ataxia). No vet writer or qualified reviewer has received any compensation from the manufacturer of the medication as part of creating this article. All content contained in this article is sourced from public sources or the manufacturer. Featured Image: iStock.com/Kateryna Kukota