Botox (onabotulinumtoxin A)​ has been extensively evaluated in double blinded, randomized studies (Level 1 Evidence) to alleviate a myriad of symptoms related to muscle spasm and over-activity, including clear indications for the treatment of migraine headaches. However, in the clinical treatment studies where patients with a diagnosed migraine disorder are treated with botox, up to 4% dropped out due to various adverse events versus 1% in the placebo group. 5% of this treatment group (32 of 687) stopped using the medication because of headache.

Unfortunately, if you are an individual who suffers from frequent migraine headaches, I quote patients a 5% risk of migraine headache induction. How long this lasts will depend on the quality and duration of your usual migraine headaches. Fortunately, this adverse event will pass and can be treated with your standard migraine medication.

Here is the link for the Botox safety data from Allergan. Page 17 has the information quoted above.