Tell your doctor if you are allergic to sulfa drugs. You may also be allergic to Flomax. When standing quickly, it may increase dizziness. Flomax can affect the pupils of your eyes during cataract surgery. You may suffer impaired thinking or reactions. Stop using Flomax and call your doctor at once if you feel like you might pass out, or if you have an erection of your penis that is painful or lasts longer than 4 hours.