The grapeseed extracts contain polyphenols which may dilate blood vessels. For the most part, this is a good thing. But some people may react to this action with dizziness or headache (mostly the chronic headache people who are sensitive and have various triggers).

Antioxidants are good for people with inflammatory issues, and some PNers may benefit from them.

There is a whole genre of supplements out there now targeting this action. Many are very expensive, and you can see benefits with less expensive but quality items.

I've used the Puritan's brand for many years, and also the one sold at Costco. We find that grapeseed extract also helps with allergies during allergy season.