Possible side effects include: transient headache, swelling, bruising, pain during injection, twitching, itching, numbness, asymmetry (unevenness), temporary drooping of eyelids or eyebrows. These side effects are rare, but have been reported. In a very small number of individuals, the injection does not work as satisfactorily or for as long as usual. Known significant risks have been disclosed, yet the theoretical risk of unknown complications does exist.