Reportedly Men's Health, blood samples have revealed biochemical evidence that intense romantic love fades after a year in a new relationship, according to a recent study in the journal Psychoneuroendocrinology. Researchers tested the blood of 58 men and women who reported being newly and madly in love, and compared the blood with samples from people in long-lasting relationships. They looked at levels of nerve growth factor (NGF), believed to be a mediator of anxiety, emotions, and behaviors. Higher NGF levels corresponded to reportedly intense feelings of passionate love. And levels were nearly double in the new lovers, compared with those in long-term partnerships. "Love is not only poetry; it also has a strong biological basis," says Enzo Emanuele, M.D., of the University of Pavia, in Italy. "An adage says that 'love is an addiction.' Perhaps we may become tolerant of our partner, though nevertheless remaining 'addicted.'"