Common side effects when used in the eyes include itchiness, redness, and a dry mouth.[1] Common side effects when used on the skin include redness, burning, and headaches.[2] More significant side effects may include allergic reactions and low blood pressure.[2][1] Use in pregnancy appears to be safe.[2][1] When applied to the eye it works by decreasing the amount of aqueous humor made while increasing the amount that drains from the eye.[1] When applied to the skin it works by causing blood vessels to contract.[2]