I found this as far as SP

saw palmetto has been known to inhibit the blood's ability to clot. This shouldn't have any bearing on your blood pressure. However, the herb could adversely interact with blood thinners, such as warfarin, clopidogrel and even aspirin.

Don't forget the salt!
http://www.mayoclinic.org/diseases-conditions/low-blood-pressure/basics/treatment/con-20032298