Spread of toxin effects; swallowing and breathing difficulties can lead to death. Seek immediate medical attention if respiratory, speech or swallowing difficulties occur. The potency Units of Letybo® are not interchangeable with other preparations of botulinum toxin products. Potential serious adverse reactions after Letybo® injections for unapproved uses. If a hypersensitivity reaction occurs, discontinue Letybo® and immediately initiate appropriate therapy. Adverse reports have been received involving the cardiovascular system, some with fatal outcomes. Use caution when administering to patients with pre-existing cardiovascular disease. Concomitant neuromuscular disorder may exacerbate clinical effects of treatment. Use with caution in patients with compromised respiratory function or dysphagia.