Okay, forgive me for being unromantic, but "love" is an emotional interpretation of the physiological effect of hormones. Three stages of love have been proposed – lust, attraction and attachment. Each stage is possibly driven by different hormones and chemicals.
(Condensed from
http://www.youramazingbrain.org/lovesex/sciencelove.htm)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~
Stage 1: Lust
This first stage of love is driven by the sex hormones testosterone and estrogen, in both men and women.
Stage 2: Attraction
In this phase, you are love-struck and can think of little else. Scientists think that three main neurotransmitters are involved in this stage:
Adrenaline
The initial stages of falling for someone activates your stress response, increasing your blood levels of adrenalin and cortisol. This has the effect that when you encounter your new love, you start to sweat, your heart races and your mouth goes dry.
Dopamine
The brains of newly love struck couples were examined. It was discovered they have high levels of the neurotransmitter dopamine. This chemical stimulates ‘desire and reward’ by triggering an intense rush of pleasure. It has the same effect on the brain as taking cocaine!
Couples often show the signs of surging dopamine: increased energy, less need for sleep or food, focused attention and exquisite delight in smallest details of the relationship .
Serotonin
This is one of love's most important chemicals and may explain why when you’re falling in love, your new lover keeps popping into your thoughts.
An experiment showed that early love (the attraction phase) actually changes the way you think. A psychiatrist tested twenty couples who'd been madly in love for less than six months to see if the brain mechanisms that cause you to constantly think about your lover were related to the brain mechanisms of Obsessive-Compulsive Disorder. Blood samples from the lovers showed that serotonin levels of new lovers were equivalent to the low serotonin levels of Obsessive-Compulsive Disorder patients.
Love needs to be blind! Newly smitten lovers often idealize their partner, magnifying their virtues and explaining away their flaws. New couples also exalt the relationship itself. It's very common to think they have a relationship that's closer and more special than anyone else's. Psychologists think we need this rose-tinted view. It makes us want to stay together to enter the next stage of love.
Stage 3: Attachment
Attachment is the bond that keeps couples together long enough for them to have and raise children. Scientists think there might be two major hormones involved in attachment:
Oxytocin
Oxytocin is a powerful hormone released by men and women during orgasm. It probably deepens the feelings of attachment and makes couples feel much closer to one another after they have had sex. The theory goes that the more sex a couple has, the deeper their bond becomes.
Oxytocin also seems to help cement the strong bond between mother and baby and is released during childbirth. It is also responsible for a mother’s breast automatically releasing milk at the mere sight or sound of her young baby.
It has been shown that if you block the natural release of oxytocin in sheep and rats, they reject their own young. Conversely, injecting oxytocin into female rats who’ve never had sex, caused them to fawn over another female’s young as if they were their own.
Vasopressin
Its potential role in long-term relationships was discovered when scientists looked at the prairie vole. Prairie voles indulge in far more sex than is strictly necessary for the purposes of reproduction. They also – like humans - form fairly stable pair-bonds. When male prairie voles were given a drug that suppressed the effect of vasopressin, the bond with their partner deteriorated immediately (they lost their devotion and failed to protect their partner from new suitors).