Research seems to suggest that acupuncture can be effective in treating high blood pressure, one study finding it as successful as drug treatment. This study did suggest though that it requires ongoing treatment and this would accord with my own experience of treating hypertension with acupuncture. Follow the link below to see summaries of relevant research:
http://www.jcm.co.uk/catalogue.php?catID=695&opener=0-691-695
