However, if you are experiencing possible side effects due to caffeine, known as caffeinism (increase in blood pressure, anxiety, nervousness, irritability, restlessness, headaches, palpitations, and insomnia), it's time to taper by cutting back.
"Slurped in black coffee or sipped in green tea, gulped down in a soda or knocked back in a headache pill, caffeine is the world’s most popular psychoactive drug.”
“Without that useful jolt of coffee-or Diet Coke or Red Bull-to get us out of bed and back to work, the 24-hour society of the developed world couldn’t exist.”
“When the nature of work changed from a schedule built around the sun to an indoor job timed by a clock, humans had to adapt. The widespread use of caffeinated food and drink-in combination with the invention of electric light-allowed people to cope with a work schedule set by the clock, not by daylight or the natural sleep cycle.”
For an excellent review on the history of caffeine, read the article by T.R. Reid in the January 2005 edition of National Geographic (all quotes above are from the article).
For adults, try to limit caffeine to 300-400 mg/day. A typical cup of brewed coffee has approximately 100 mg of caffeine (a cup is 8 ounces and most of us drink out of mugs that hold 2-4 cups).
Learn the approximate amount of caffeine in coffee, tea, soda, energy drinks, sweets and medications (mayoclinic.com/health/caffeine is an excellent source).
Remember that moderation is still probably the best and healthiest practice.
If you're someone who drinks caffeine all day, now's a good time to start cutting back.