Does Love Exist? Science has the answer

Serotonin - Scientists think serotonin probably decreases at this stage, but more studies need to be done. Low levels of serotonin are found in obsessive-compulsive disorder (OCD) and are thought to cause obsessive thinking. In one Italian study of 60 students, those who were recently in love and those with OCD both had less serotonin transporter protein in their blood than regular (not recently in love) students.