In the mid-1990s, people who received BOTOX for other conditions reported improvement in their chronic migraine pain. A two-phase study was conducted, treating patients who averaged 20 headache days a month. They received BOTOX injections every twelve weeks for 56 weeks. At the end of that period, 70% of the patients had fewer than half the number of headaches they had before treatment. The FDA officially approved BOTOX to treat chronic migraine in October of 2010. Since then, more than 100,000 patients have been treated.
Spread of toxin effects. The effect of botulinum toxin may affect areas away from the injection site and cause serious symptoms including: loss of strength and all-over muscle weakness, double vision, blurred vision and drooping eyelids, hoarseness or change or loss of voice, trouble saying words clearly, loss of bladder control, trouble breathing, and trouble swallowing.