Because caffeine is primarily an antagonist of the central nervous system's receptors for the neurotransmitter adenosine, the bodies of individuals who regularly consume caffeine adapt to the continual presence of the drug by substantially increasing the number of adenosine receptors in the central nervous system. This increase in the number of the adenosine receptors makes the body much more sensitive to adenosine…
Because adenosine, in part, serves to regulate blood pressure by causing vasodilation, the increased effects of adenosine due to caffeine withdrawal cause the blood vessels of the head to dilate, leading to an excess of blood in the head and causing a headache and nausea. Reduced catecholamine activity may cause feelings of fatigue and drowsiness. A reduction in serotonin levels when caffeine use is stopped can cause anxiety, irritability, inability to concentrate and diminished motivation to initiate or to complete daily tasks; in extreme cases it may cause mild depression. Together, these effects have come to be known as a "crash".
Withdrawal symptoms—possibly including headache, irritability, an inability to concentrate, drowsiness, insomnia and pain in the stomach, upper body, and joints—may appear within 12 to 24 hours after discontinuation of caffeine intake, peak at roughly 48 hours, and usually last from one to five days, representing the time required for the number of adenosine receptors in the brain to revert to "normal" levels, uninfluenced by caffeine consumption. Analgesics, such as aspirin, can relieve the pain symptoms, as can a small dose of caffeine. Most effective is a combination of both an analgesic and a small amount of caffeine.
The stupid thing is that I'm only doing this because a little voice in my head says I should be. It's not like my over-consumption of Diet Coke has been having any kind of negative effect on my day to day existence, I just don't like the idea of being addicted to something.
In other news: Boing Boing: how to make smokable freebase caffeine from ground coffee and ammonia.
I also go through about a week every year where I try to go caffeine-free.
One side-effect I've noticed is that, after going without for a while, is that the potency of caffeine is increased for me when I start up again. This in itself is a benefit that justifies the week or so of annoyance.
See also The Calculus of Caffeine Consumption
At the risk of sounding like a wet blanket, Charles, I say "drink more water, exercise more and sleep more". Easier said than done, I know.
We're addicted to air, water, food and love a couple of extra addictions can't possibly hurt. ;-)
This is me trying to justify me drinking too much (wine|beer|coffee).
Did the same thing, stopped caffeine intake. Had 3 days of headaches and then I was fine. I started up again a few weeks later and really I didn't notice much of a difference.
But I do like the taste of coffee.
I went off coffee just before the new year because I had an incredibly annoying eye twitch since mid-November and it seemed to get exponentially worse when I drank coffee. I still drink a bit of caffeinated tea during the day (partly to keep warm in my sub-zero office!), but I'm off the coffee.
It's so odd - I feel better than ever in the mornings. I no longer need coffee to get me going, and I don't crave it anymore. I would have never believed I could do it...