Parablemania: The Science of Love: "three levels of what broadly might be called love: lust, romantic love, and long-term attachment. (In my terms, these would be lust, romantic infatuation, and love. I don't see the second kind as really love, though it's often blindly called that by younger people who have never experienced love.) Lust is a craving for sex, and lustful sex leads to a brain state similar to an opium high. Infatuation has 'feelings of exhilaration, and intrusive, obsessive thoughts about the object of one's affection.' This is commonly called 'being in love' in high school and even in college. The brain state here doesn't resemble an opium high but is more like the more permanent brain states of someone with Obsessive-Compulsive Disorder. Finally, there's what I would say is love, a permanent attachment. The brain state here is similar to what's associated with 'feelings of calm, security, social comfort and emotional union.' "