Since then, several randomized control trials have shown botulinum toxin type A to improve headache symptoms and quality of life when used prophylactically for patients with chronic migraine[88] who exhibit headache characteristics consistent with: pressure perceived from outside source, shorter total duration of chronic migraines (<30 years), "detoxification" of patients with coexisting chronic daily headache due to medication overuse, and no current history of other preventive headache medications.[89]
The primary efficacy variable was wrist flexors muscle tone at week 6, as measured by the Ashworth score. The Ashworth Scale is a 5-point scale with grades of 0 [no increase in muscle tone] to 4 [limb rigid in flexion or extension]. It is a clinical measure of the force required to move an extremity around a joint, with a reduction in score clinically representing a reduction in the force need ed to move a joint (i.e., improvement in spasticity).

BOTOX, highly diluted botulinium toxin, works to prevent migraine by blocking the release of a chemical in muscle cells that transmits the signal to contract to muscle fibers. Research into using BOTOX to treat migraines began after patients receiving it for other conditions reported improvement in their migraine symptoms. In 2010, after years of research and collecting clinical data, the FDA approved BOTOX for treating chronic migraines.

Serious and/or immediate hypersensitivity reactions have been reported. These reactions include anaphylaxis, serum sickness, urticaria, soft-tissue edema, and dyspnea. If such a reaction occurs, further injection of BOTOX® should be discontinued and appropriate medical therapy immediately instituted. One fatal case of anaphylaxis has been reported in which lidocaine was used as the diluent, and consequently the causal agent cannot be reliably determined.
BOTOX® treats the symptoms of severe underarm sweating when topical medicines do not work well enough in people 18 years and older. It is not known whether BOTOX® is safe or effective for severe sweating anywhere other than your armpits. BOTOX® treatments temporarily block the chemical signals from the nerves that stimulate the sweat glands, resulting in reduced sweating.