Most of the side effects of the lidocaine patch affect the skin that has been treated with lidocaine. Possible side effects include blisters, redness, swelling and changes in skin color. These side effects usually dissipate within a few minutes or hours of application. If a burning sensation or persistent irritation occurs, remove the patch and do not apply a new one until the sensation has gone away. Serious die effects include blurred vision, drowsiness, nervousness, unusually slow heart beat and dizziness. These serious side effects should be reported to a doctor immediately.