Onabotulinum toxin A (Botox) is approved by the FDA for the treatment of chronic migraine, not tension type or episodic migraine.
Chronic migraines are characterized with:
-a headache syndrome for more than 3 months
-at least 15 or more headache days per month
-headache experienced for at least 4 hours
-headache experienced for at least 8 months
Onabotulinum toxin A inhibits neurotransmitter (acetylcholine) release, disruption of neuromuscular transmission, and paralysis of the muscle injected. Acetylcholine is blocked from carrying pain signals from the brain to nerve endings of the muscle.
Muscle paralysis produced by Botox treatments lasts for a few months, so repeated injections may be necessary. A successful injection will result in a reduction of headache days.