Histamine Intolerance(HI) Is Common Histazyme features DAO, which actually breaks down histamine. If you have an issue with histamine intolerance from ingested histamine, try Histazyme today.† Histamine Intolerance Is A Common Problem Histamine Intolerance (HI) is more common than you may think. I can’t tell you how often I speak with patients and discover that the source of many of their routine complaints, such as mild headaches and other inconveniences, turns out to be histamine intolerance. After lab testing rules out other issues, I often find that the mysterious source boils down to this sometimes difficult-to-detect sensitivity to ingested histamine from foods.