Lovers are obsessed. And doctors who treat individuals with most forms of obsessive-compulsive disorder prescribe SSRIs (selective serotonin reuptake inhibitors) such as Prozac or Zoloft, substances that elevate levels of serotonin in the brain. So I came to suspect that the lover´s persistent, involuntary, irresistible ruminations about a sweetheart might be associated with low levels of some type (there are at least fourteen variations) of this chemical compound.

Why We Love, S. 54