MSG is a migraine trigger according to the Journal of
the American Medical Association:
http://www.hmc.psu.edu/childrens/healthinfo/articles/migraines.pdf
The fact that MSG is a migraine trigger is not
surprising when you consider that glutamate - the business end of MSG is a
calcium channel opener. (Most blood pressure lowering medications are
calcium channel blockers). MSG therefore affects blood vessel
vasoconstriction.
Also, there is a theory that migraines are caused by
inflammation in the mouth area pressing against nerves in the head. It
must be mentioned here that glutamate increases histamine response although
it does not initiate an immune antigen response. Histamine induces
inflammation.
These two items - blood vessel vasoconstriction and
inflammation are implicated in migraines and are also caused by ingestion of
MSG.
Below is a story about a physician who treats his
migraine patients with an MSG-free diet:
http://www.npr.org/templates/story/story.php?storyId=5364970