There are three chemicals associated with the early stages of love:
Serotonin: Can't eat? Can't sleep? Can't quit thinking about your love? Blame seratonin. This hormone does a bit of everything, from telling your body if it's getting enough food to causing dominant and obsessive/compulsive behavior. In some species, a large surplus of food will increase seratonin production, telling the animal to switch from finding food to finding a mate.
Phenylethylamine (PEA): This is a stimulant similar to an amphetamine, and it causes the release of norepinephrine and dopamine. It's present in chocolate, which is why some people say eating it gives one the the feeling of falling in love.
Norepinephrine: This stress hormone is tied to the fight-or-flight reaction and makes your heart race.
After a while these taper off and new chemicals come into the picture:
Nerve growth factor (NGF): This protein supports the growth and repair of neurons. It's found in heightened levels within the first year of their relationship, and then slowly tapers off.
Oxytocin: Scientists have yet to uncover all of the effects of this hormone, but we do know it is linked to several stages of pregnancy and early motherhood, from labor to milk production. It's also released during orgasm. Higher overall levels are found in long-term couples.
Endorphines: These opiate-like chemicals are released into our brains in short bursts when we're excited, perform strenuous exercise, have sex, or relax. When we're in love for a long period, endorphines are slowly released as long as we're around our partners. This steadily increases the longer they're together, forming the chemical basis of long-term love. MRI tests have shown increased activity in the part of the brain that releases dopamine when someone sees the person they're in love with.
Posted 1122 day ago