Theobromine makes up 1 to 2% of cacao powder and dilates blood vessels as it stimulates the nervous system. This is too much for humans sensitive to caffeine. If you have anxiety or sleep problems, cacao powder can negatively affect those issues. Be aware that cacao powder also contains a high amount of fat and calories if you’re on a restrictive diet. Some people have an allergic reaction to chocolate — if this is you, avoid cacao powders altogether.