trimethylxanthine

Caffeine is one if, if not the most under acknowledged drugs that exists in my opinion.  It is also extremely popular among humans & can have many different effects based on how many milligrams of it is consumed.  

Caffeine is known medically as trimethylxanthine, its chemical formula is C8H10N4O2.  It operates using the same mechanisms that amphetamines such as Cocaine & Heroine to stimulate the brain.  Luckily, for 90% of Americans who consume Caffeine, its effects are much milder than those of amphetamines 

Typical Amounts of Caffeine contained within various substances:

Effects of Caffeine, based upon my own experience include: 

• temporary heightened alertness 
• feeling of sluggishness afterwards 
• desire to consume more caffeine 
• periods of stress during consumption 
• periods of heightened energy
• speed of heart beat increases

Additional Effects of Caffeine, obtained from www.howstuffworks.com/caffeine3.htm:

• Dilation of Pupils
• Opening of Breathing Tubes (can be dangerous for asthmatics)
• Blood vessels on the surface constrict so as to slow blood flow from cuts & increase blood flow to the muscles.
• The Liver releases sugar into the bloodstream for extra energy
• Muscles tighten up

As adenosine is created, it binds to adenosine receptors.  The binding of the adenosine to the receptors is what causes sleep.  To a nerve cell, caffeine appears to be adenosine, it then binds to the receptor, however unlike adenosine, the caffeine does not slow down the receptor's activity, thus the receptor is unable to 'see' and speeds up.  Caffeine may cause certain blood vessels in the head to constrict by blocking the adenosine's ability to open them up.

As a direct result of the speeding up of neurons in your brain, your pituitary gland perceives this as some kind of emergency and it releases adrenaline into your body, which explains the above listed effects.

Caffeine increases dopamine levels in the same way that amphetamines do (by slowing down the rate of dopamine reuptake).  Dopamine is a neurotransmitter that in certain parts of the brain activates the areas of the brain, which signify pleasure.