Amongst many of the conclusions, the study summarized that: "If effective and available, non-pharmacological treatments may be the first choice for most patients and may also be well suited for the significant minority of patients who: (a) have poor tolerance of pharmacological treatments; (b) have medical contraindications for pharmacological treatments; (c) experience insufficient relief from, or are unresponsive to, pharmacological treatment; (d) wish to become pregnant (or are nursing); (e) have a history of long-term, frequent, or excessive use of analgesic or abortive medications that can aggravate headache problems; or (f) simply prefer to avoid medication use".

Conclusions With Regard to Chiropractic:

• Cervical manipulation was associated with significant improvements in headache outcomes in trials involving patients with neck pain and/or neck dysfunction and headache. 

• Adverse effects are uncommon with manipulation, and this may be one of its appeals over drug treatment.

• Manipulation is effective in patients with cervicogenic headaches...

McCrory DC, Penzien DB, Hasselblad V, Gray RN. Evidence Report: Behavioral and Physical Treatments for Tension-type and Cervicogenic Headache. Duke University Evidence-based Practice Center for Clinical Health Policy Research. - 2001