My dad started to drink a lot of green tea, actually 4 cups a day and these are actually large cups, so it's probably like 8 cups and he said he noticed he started to have issues with his blood pressure again, so he's scaling back.

So I googled for awhile and I can only find benefits of green tea and blood pressure. When I google the things that come up often are body weight, cholestrol and blood pressure as improvements.

I tried to find as many studies as possible and I can only find things that were positive for blood pressure as well as studies that say it's inconclusive.

Any opinion on if it helps, hurts or does nothing for blood pressure?

Too much of a good thing. It's good that he is scaling back. Tea does have caffeine. Too much caffeine can raise heart rate and blood pressure. Tannin is good for you, but remember that it interferes with mineral absorption, especially zinc, calcium, and iron. Tannin also interferes with protein digestion. So he should enjoy his tea away from food.

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- Jim
Life is just one damned thing after another - Elbert Hubbard

I'm not convinced it's the green tea

Increases in Blood Pressure and Heart Rate Induced by Caffeine are Inhibited by (-)-Epigallocatechin-3-O-gallate: Involvement of Catecholamines

Then it could be the tannin. Tannin can interfere with some medications. Is your father on any medications? Also, tannins are drying. Too much tea can make me constipated due to the drying and binding aspects of tannin. He should drink plenty of water anyway. Dehydration can be bad for blood pressure among other things.