A recent post from Bob, our resident research guru:

Handb Clin Neurol. 2010;97:217-32.
Botulinum neurotoxin in the treatment of headache disorders.
Mauskop A.
Abstract
Botulinum neurotoxin (BoNT) has been in clinical use for the treatment of headaches for over 15 years. Recent double-blind placebo-controlled trials have confirmed the efficacy of BoNT type A (onabtoulinumtoxinA, Botox) in the treatment of chronic migraine.

THE EFFICACY OF BONT IN THE TREATMENT OF EPISODIC MIGRAINE HEADACHES, CLUSTER HEADACHES, AND CHRONIC TENSION-TYPE HEADACHE (TTH) HAS NOT BEEN EXAMINED IN LARGE CONTROLLED TRIALS.

Presumed mechanisms of action of BoNT in headache disorders are the reduction of afferent input induced by muscle relaxation and inhibition of the release of neurotransmitters, such as glutamate and calcitonin gene-related peptide, from peripheral sensory nerve terminals. Over 20 years of extensive clinical experience has established a remarkable safety for BoNT, particularly type A and specifically Botox or onabotulinumtoxinA, which has been used much longer and more widely than any other form or serotype of BoNT. Because BoNT is a biological product, the safety and efficacy of one BoNT formulation cannot be extrapolated to a different one, even of the same serotype.

Copyright © 2011 Elsevier B.V. All rights reserved.

PMID:20816423[PubMed

And a paper Batch posted on the same topic:

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Hope this helps, been a mixed bag on people who tried it. Worked wondres for some, worthless for others. Ahhh.. the nature of CH!

Joe