There is one drug that is abused more than any other by humanity.  It is an addictive and psychoactive stimulant that was very nearly made illegal in the US in the 1920s.  Users report a unique feeling of energy, euphoria, and alertness while on the drug.  Users can also suffer withdrawal symptoms including, headaches, muscle pain, insomnia, dysphoria and irritability.  In high doses this drug can be fatal, and 90% of Americans and 80% of human being use it every day.  This productivity drug is caffeine. First, where did caffeine come from?  Why was the development of this chemical an evolutionary advantage?  The reason that this chemical is so prevalent in the natural world is also the key to its cultivation and usage by humans.  In moderate doses the chemical acts as a pesticide.  This advantage aids the plant, as insects who attempt to eat the plant are killed.  Additionally, pollinating insects, such as honeybees, receive small doses of the chemical.  Through this dose, the desire to continue pollinating the plant increase.  The honeybees receive similar euphoric stimulation as mammals do.  Why pollinate flowers that don’t get you high?  Ancient humans discovered the effects of the chemical through both chewing on and brewing the leaves of certain plants.  Since then humans have been using caffeine for its stimulating and euphoric effects. Adenosine is the key to caffeine’s effects on the brain and body.  Adenosine is an inhibitory neurotransmitter existing in large concentrations within the body.  It works by binding to neurons and slowing down their functions like applying a brake to a moving car.  Caffeine binds to these receptors but does not cause the inhibiting affects.  This results in the neurons operating faster than normal, essentially releasing the brake.  Other than general neurons, caffeine also affects dopamine and serotonin neurotransmitters, again by blocking out adenosine.  The effects lead to a euphoria, increased alertness, greater metabolic rate, and decreased fatigue.  Caffeine can also improve athletic performance, by decreasing fatigue and pain.  Unfortunately, after prolonged use the body will develop a partial immunity to caffeine.  The brain, which loves operating at equilibrium, will add additional adenosine receptors to neurons.  As a result it requires more adenosine to achieve the desired neural inhibiting effects.  Like any drug over time the user will be required to take more caffeine to receive the same high.  Withdrawal symptoms occur when the overabundance of adenosine receptors are activated by the body’s supply of adenosine.  Too much bound adenosine leads to over inhibition of neurotransmitters and leads to an effect which is opposite of the previous high.  Withdrawal symptoms include dysphoria, insomnia, drossiness, headaches, and muscle, joint, and stomach pain.  The symptoms usually peak after 48 hours and can last up to two weeks.  The brain adapts to the lack of previous levels of bound adenosine in the neurons and absorbs excess receptors returning the brain to equilibrium. Caffeine, much like its sister stimulants cocaine and amphetamine, has profound effects on the mind and body.  It can improve alertness, banish drowsiness, and improve athletic performance.  However, like any chemical, understanding its effects and using it intelligently is key.  It can improve your mood and productivity, but abuse comes at a price.  Through better knowledge of our bodies and the chemicals we ingest, we can create a better, happier world.   Sources: Levinthal, C. F. Drugs, Behavior, and Modern Society, 6th ed., Allyn and Bacon, Boston “Mouse Party”