Oxytocin, the love/hate hormone
You may have heard of oxytocin, sometimes called the "love hormone." Human and animal studies have shown that oxytocin plays a role in bonding; when released in your brain during certain types of human contact, it has the effect of bonding you to the other person involved. This makes a lot of sense, because oxytocin is known to be released when a woman is nursing her infant, when two people are hugging, and during sexual activity. It's also thought to be involved in other corollary emotional responses of bonding, like trust-building and empathy. Some early research has suggested that oxytocin could be used therapeutically in people who suffer from disorders like autism or schizophrenia, which hinder bonding and positive relationship development. In studies, applying a dose of oxytocin via nasal spray showed promise in such patients.
However, things are never as simple as they seem, and more recent research on oxytocin suggests a dark side to the so-called "love hormone." While affecting positive behaviors of trust and bonding, it can also affect opposite behaviors like jealousy, envy, and suspicion. This would suggest that contrary to prior belief, oxytocin triggers and amplifies social feelings of all types, not just the positive, feel-good ones. In the words of researcher Simone Shamay-Tsoory of the University of Haifa, "…when the person's association is positive, oxytocin bolsters pro-social behaviors; when the association is negative, the hormone increases negative sentiments". According to psychologist Greg Norman, this shows that "oxytocin is not a love hormone; its effects vary in different people." So maybe we should hold off on that nasal spray thing for the time being.
http://www.brainhq.com/brain-resources/brain-facts-myths/brain-in-love