Cocoa solids are one of the richest sources of flavanol antioxidants.[3] They also contain alkaloids such as theobromine, phenethylamine and caffeine.[4] These have physiological effects on the body and are linked to serotonin levels in the brain. Some research has found that chocolate, eaten in moderation, can lower blood pressure.[5] The presence of theobromine renders chocolate toxic to some animals,[6] especially dogs and cats.