Caffeine Withdrawal
Have you ever tried to cut back on your favorite brew or switched to decaffeinated only to find out that you feel lousy? Well, you may be experiencing caffeine withdrawal.

Headaches are the main symptom you are likely to develop. Others become depressed, anxious, or fatigued and some even complain of flu-like symptoms and nausea.

Symptoms appear 12 to 24 hours after your last dose of caffeine. The symptoms generally peak on the second day but may last for up to a week. 

Sources of caffeine include caffeinated soda, tea and some medications. Two to four cups of tea or two to four cans of caffeinated soda can provide as much caffeine as one to two cups of regular coffee------enough to cause withdrawal symptoms in susceptible individuals if they skip their beverage for as little as just half a day.  

Medications
Medications containing caffeine can also create a dependency, triggering a reaction when you stop taking it.

Drug Interactions
A variety of drugs---including birth control pills, the heart drug Verapamil (Calan, Veleran) and the ulcer or heartburn drug, Tagamet, can diminish the body's ability to rid itself of caffeine. As a result, even low doses of caffeine combined with any of these medications can cause insomnia, irritability or heart palpitations.

Medications that stimulate the nervous system---including appetite suppressants, asthma drugs, thyroid hormones, and oral decongestants--- also add to the effects of caffeine.