How does botulinum toxin work in chronic migraine?
The simple answer is that we don’t know fully. A recent US study by Rami Burstein et al using animal models suggested that botulinum toxin inhibits pain in chronic migraine by reducing the expression of certain pain pathways involving nerve cells in the trigeminovascular system. The trigeminovascular system is a sensory pathway thought to play a key role in the headache phase of a migraine attack.Unlike many of the other conditions in which it is used, it is not thought to work by relaxing overactive muscles. Botulinum toxin has been shown to reduce pain in a number of disease states, including cervical dystonia, neuropathic pain, lower back pain, spasticity, myofascial pain, and bladder pain.More research into the mechanism of action of botulinum toxin will hopefully shed light into all the pathways that it acts upon.
Is Botox® right for me?
  Only patients with chronic migraine are eligible for treatment with Botox®. Chronic migraine is defined as headaches occurring on 15 or more days each month, at least half of which have migrainous features. There are, however, other treatments available to patients with chronic migraine, and it is important that patients have an informed discussion of their headaches and the options for treatment with a practitioner experienced in the diagnosis and management of headaches before a decision to use Botox® is taken.

Who can inject Botox® for chronic migraine?
At present the use of Botox® is restricted to a few specialist headache centres, but as time goes on there should be increasing numbers of trained injectors available. In all cases, however, you should ensure that the person injecting has received appropriate training, both in the diagnosis and management of chronic migraine, and in the delivery of Botox® according to the proven PREEMPT schedule. Please note that the referral process differs for each location.  In the first instance, patients who are struggling to manage their symptoms should discuss this with their general practitioner (GP) and if appropriate, seek referral to a specialist with an interest in headache disorders.  Read more about seeking medical advice.On visiting a migraine clinic a detailed history of the patient’s condition will be taken, including symptoms, frequency of attacks and any medication tried in the past or currently taking.  Keeping a diary can help with this.
Availability of Botox® for treating chronic migraine on the NHS