Botox does have potential side effects, though they are relatively rare. In clinical trials, the most common side effect was neck pain, which was reported by 9% of those who used BOTOX. Other less common side effects included headache, migraine, slight or partial facial paralysis, drooping eyelids, bronchitis, musculoskeletal stiffness, muscular weakness, muscle pain, musculoskeletal pain, muscle spasms, injection site pain, and high blood pressure.