There is no research to support the use of barley green which is manufactured from barley grass as a herbal supplement. There is no nutrient analysis with the caffeine content of barley green so I can’t tell you if barley green has caffeine or not. Also, I can’t tell you if barley green has any effect (positive or negative) on your headaches due to the lack of research.
Barley, a harvested grain from mature grass, does have soluble fiber which helps lower total and LDL cholesterol. You can find barley in Grape Nuts cereal, pearl barley which can be added to soups or stews or barley flakes added to bread and muffins. Barley malt is used in the manufacture of beer.