Because Botox works by temporarily paralyzing certain muscles, there are some side effects patients should be aware of before undergoing Botox treatments for neck pain.  Common side effects may include muscle weakness near the injection site, difficulty swallowing, muscle stiffness, dry mouth, loss of appetite, among others.  You may also notice bruising, swelling, or redness at the injection site. As with any time the skin is pierced by an injection, there is a chance for infection. Most patients will only experience mild injection site side effects that will dissipate within a few hours or days.