We all remember that first cup of coffee; it tasted terrible. It was too hot, too bitter and too sweet but it offered the promise of alertness after a night of poor sleep.

The wonderful thing about coffee is that it delivered on its promise every time; subsequently, you've never been able to walk away from it. If you've ever faced giving up on caffeinated coffee to lessen the symptoms of fibrocystic breast disease of the tremors associated with Parkinson's disease you know well the craving that can develop.

Why does this happen?

Two reasons: Scientists have known for many years that coffee stimulates the release of the neurotransmitter . Dopamine produces the euphoria and pleasant feelings that people often associate with their first cup of coffee in the morning.

Many drugs that produce euphoria, such as , and ecstasy, act upon dopamine in the brain. This action by coffee has always been an adequate explanation for why is the most widely consumed psychoactive substance in the world.

But do we all really just crave more arousal? Is being more aroused enough to explain why for some people coffee is akin to cocaine — they crave it constantly and will work hard to have a supply always at hand?

One of my students decided to test the effects of caffeine on his chronic sleepiness by ingesting a packet of instant coffee, right out of the box. He reported that he enjoyed eating this paper packet of ground coffee so much that he decided to finish off the entire container of 32 packets! Three days later, he stopped having explosive diarrhea and finally fell asleep completely exhausted.

Another of my students claimed to consume two full pots of coffee (equivalent to about 20 cups of coffee!) every morning before coming to class. He indicated that he knew it was time to stop when the tremors in his hands became impossible to control.

These students' experiences remind me of the verses of the French novelist Honore de Balzac: "This coffee plunges into the stomach...the mind is aroused, and ideas pour forth like the battalions of the Grand Army on the field of battle...Memories charge at full gallop...the light cavalry of comparisons deploys itself magnificently; the artillery of logic hurry in with their train of ammunition; flashes of wit pop up like sharp-shooters."

To me, these behaviors suggest a level of that goes beyond the simple enhancement of one neurotransmitter system.

A recent report in Molecular and Food Research by a group of scientists from Rome explored the possibility that coffee's addictive properties also involve the brain's -like neurotransmitter system. [I've previously written about the role of this system in control mood and general brain function; here are the links: A, B, C.] This is how it all seems to work.

When you first started drinking coffee, the arousal was all you wanted and also all that you got. Still, being more attentive and vigilant was all you needed to get through the day.

As you continued drinking coffee, your liver compensated for the additional chemicals in your diet by becoming more efficient at metabolizing the caffeine. Your brain also made some adjustments. Ultimately, you needed more and more coffee each day to achieve the same level of arousal and vigilance.

While all of this was occurring, something else far more mysterious was happening inside your brain; caffeine had begun stimulating your brain's endogenous marijuana neurotransmitter system. These biochemical adjustments introduced an entirely new level of pleasure to your morning cup of java. In addition, it made avoiding that third or fourth cup of coffee even harder to accomplish.

Coffee makes us feel so good because it is able to tap into virtually every reward system our brain has evolved. Hidden within that hot elixir is a chemical that takes over your brain by mimicking the actions of cocaine and marijuana.

It's too late — go ahead and have another cup. I'm going to.

© Gary L. Wenk, Ph.D., author of Your Brain on Food

Also see: Marijuana and Coffee Are Good for the Brain.

I was recently honored by an invitation to give a TED talk on the benefits of coffee and other drugs upon brain function. The video is available here.