In double-blind, placebo-controlled chronic migraine efficacy trials (Study 1 and Study 2), the discontinuation rate was 12% in the BOTOX treated group and 10% in the placebo-treated group. Discontinuations due to an adverse event were 4% in the BOTOX group and 1% in the placebo group. The most frequent adverse events leading to discontinuation in the BOTOX group were neck pain, headache, worsening migraine, muscular weakness and eyelid ptosis.

Autonomic dysreflexia in patients treated for overactive bladder due to neurologic disease. Autonomic dysreflexia associated with intradetrusor injections of BOTOX® could occur in patients treated for detrusor overactivity associated with a neurologic condition and may require prompt medical therapy. In clinical trials, the incidence of autonomic dysreflexia was greater in patients treated with BOTOX® 200 Units compared with placebo (1.5% versus 0.4%, respectively).
OnabotulinumtoxinA is the only treatment approved by the United States Food and Drug Administration for the prevention of headaches in adult patients with chronic migraine (CM). CM assessment involves a detailed history to rule out secondary sources of headache, establish migraine features, and assess the total number of headache days. In order to diagnose migraine, the patient should have had at least five attacks that involve migraine features, as outlined below. In adults, untreated attacks usually last 4 or more hours.
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.