Possible side effects and unwanted results include Pain, swelling, or bruising at the injection site. Headache or flu-like symptoms. Droopy eyelids or crooked eyebrows. Selecting a licensed medical aesthetician when getting injections in your facial muscles is crucial. Over-injection can cause the muscles that control your smile to stop working properly, which can give you a “paralyzed” look. More severe cases can even lead to difficulty speaking or eating. Assessing these muscles accurately is a complex process.