Love is a chemical state of mind. Scientists has proposed 3 stages of love, with each driven by different formulas of hormones and chemicals. The chemicals that race around in the brain when in love serve several purposes but primary goal is the continuation of our species.
 
Stage 1: Lust
This stage is driven by the sex hormones testosterone and oestrogen, in both men and women.
 
Stage 2: Attraction
This is the amazing time when you are truly love-struck and can think of little else, is the biological drive to focus on one person. 

The three main neurotransmitters 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 charming effect that when you unexpectedly bump into your new love, you start to sweat, your heart races and your mouth goes dry.
 
Dopamine
Helen Fisher asked newly ‘love struck’ couples to have their brains examined and 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!

Serotonin
One of love's most important chemicals that may explain why when you’re falling in love, your new lover keeps popping into your thoughts.
 
Stage 3: Attachment
Attachment is the bond that keeps couples together long enough for them to have and raise children. 

The two major hormones involved in this feeling of 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 mum and baby and is released during childbirth. It is also responsible for a mum’s breast automatically releasing milk at the mere sight or sound of her young baby. 

Diane Witt, assistant professor of psychology from New York has showed 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, nuzzling the pups and protecting them as if they were their own.
  
Vasopressin
Vasopressin is another important hormone in the long-term commitment stage and is released after sex. Vasopressin (also called anti-diuretic hormone) works with your kidneys to control thirst. Its potential role in long-term relationships was discovered when scientists looked at the prairie vole.