While side effects are certainly not common, three percent of patients experienced eyelid drooping in studies where frown lines were being treated. In studies where crow’s feet were being treated, one percent of the patients experienced some swelling in the eyelid. Some other possible side effects include pain or discomfort at the site of the injection; dry mouth; fatigue; headache; neck pain; and vision problems, such as double or blurred vision, decreased eyesight and dry eyes. There is also a small risk for allergic reactions.