But quitting isn't easy. It can be so hard, The Early Show consumer correspondent Susan Koeppen reports, that some people are now going into caffeine rehab.
Koeppen tells of a recent Friday morning in Baltimore, when all Lynda Davis can think about is getting her fix.
"I have a strong craving for coffee," she says. "I like the taste of it, the smell of it brewing, the sound of it brewing, everything."
Davis is a caffeine addict, so hooked, she literally can't go a day without drinking coffee. Every morning, she fills up a 20-ounce travel mug to the brim.
"If I don't have it," she says. "I feel very irritable, depressed, the headache is severe, I feel down."
Davis says she's tried to quit, but failed.
She says, "I still wanted it all the time; I was thinking about it, craving it, obsessing about it day and night; and wanting it, why can't I have it? And that's when I felt like an addict."
Today, caffeine is the most commonly used mood-altering drug in the world. Nobody knows that better than addiction expert Dr. Roland Griffiths.
Griffiths says, "We know about 80 percent of the population consumes caffeine, so we have millions and millions of people out there who are physically dependent."
Many people need caffeine to jumpstart their day and get rid of that dragging feeling. Turns out, that tired feeling may really be a symptom of caffeine withdrawal.
Dr. Griffiths explains, "They don't recognize that that boost they get in the morning from that first cup of coffee or soda is actually a reversal of low-grade withdrawal effects."
Experts say all it takes is one small cup of coffee a day to get hooked. Caffeine is so powerful that some people, when they try to quit, experience withdrawal symptoms similar to those of illegal drugs like heroin and cocaine.
Dr. Griffiths says, "They'll actually have nausea, vomiting, muscle aches, and weakness."
At Johns Hopkins Medical Center, Griffiths has set up a caffeine addiction clinic to help java junkies like Lois Smith kick the habit.
Smith says, "I'd wake up and my first thought was, 'Get to Starbucks and get a cup of coffee' so I could take it to work."
At the peak of her addiction, Smith was downing up to 12 cups of coffee a day. Getting her fix began to interfere with her life.
Smith says, "There were times when my husband and I would go out to dinner after work and I would pick a restaurant because I knew that there was a Starbucks on the route."
After seeing an ad for the caffeine addiction clinic, Smith knew it was time to try to kick her habit once and for all.
At the clinic, doctors first measure how patients are getting their caffeine and how much. While most of our caffeine comes from coffee and soft drinks, you can also find it in tea, chocolate, and over-the-counter medications. The key to kicking the habit? Don't go cold turkey. At the clinic, patients have their caffeine intake cut back gradually.
Smith says, "The first week, I could only have 75 percent of what I was used to drinking; the second week, I could have 50, and so forth."
After six weeks, Smith was caffeine-free. Immediately, she noticed the benefits.
She says, "Now I wake up, I'm more rested, I'm more alert."
But in our caffeine-obsessed world, Smith knows staying clean can be a daily struggle. Koeppen took her to a local coffee shop to hear how she copes.
"Every once in awhile I'm a little shaky," Smith says. "What I try to do is, before I come in, I make up my mind that I'm not gonna get a caffeinated beverage."
Her new drink of choice? Decaffeinated herbal tea.
Smith says, "I think, I might enjoy that one cup of coffee, but then I remember the withdrawal symptoms. I just tell myself that it's not worth just having one cup."
Lynda Davis learned that the hard way. She went through the caffeine addiction clinic, and also kicked the habit. On her six-month anniversary, she rewarded herself with a cup of coffee. She says that's all it took to get hooked again.
"It makes me worry," Davis says. "I wish I could just enjoy it and not worry about it. It's best not to start it, because it's too easy to get hooked."
Experts say caffeine is not linked to any life-threatening illnesses, but it can cause things like mood swings, and insomnia.-->
Eighty to 90 percent of people in the United States use caffeine. And that means that millions of them are physically dependent.
Tune in Friday morning to find out more as Koeppen talks to addiction expert, Dr. Roland Griffiths at Johns Hopkins Medical Center in Baltimore. He not only studies caffeine addiction, he opened a caffeine addiction clinic.