In 2009, the FDA conducted a thorough safety evaluation and decided that all botulinum toxins, including Dysport, should carry a boxed warning  (as does Botox). This alerts people that these products can spread from the injection site to other areas of the body, leading to severe and life-threatening risks. These risks include difficulty speaking, swallowing, or breathing, muscle weakness, drooping eyelids, and blurred or double vision. Please read about these and other potential risks here. However, the most common but rare possible side effects include: Nose and throat irritation Headache Injection site pain Injection site skin reaction Upper respiratory tract infection Eyelid swelling Eyelid drooping Sinus inflammation Nausea