In retrospect, my joyful discovery of caffeine back in college, my junior year at UNH (university of New Hampshire) was a revelation. That first cup of tea allowed me to focus and gave me a pleasant energy boost. I went on to experiment with soda's and caffeine pills, like no-doz and vivarin. Discovered my limits, obviously, and used accordingly. Except for one instance, it never bothered my sleep patterns. As a nursing assistant working night shifts on the weekend, I used whatever had good amounts of caffeine to get thru the shifts. Same, after I got my nursing degree and worked relief nights, Moxie was my favorite beverage, especially at the 4 am "wall".
After Amber was dx'd with ADD and put on ritalin, I started to wonder about myself. So I consulted with my wife (pharmacist) and then the Doctor and started taking ritalin. WOW, the results were great, mad me wish I had this option 50 years ago. Anywho, I digress, my caffeine intake has dropped since starting ritalin. And I rarely touch soda's anymore.. I do enjoy a hot mug of Lapsang Souchong tea every morning and a couple of cups of hot black tea when the weather gets colder. Coffee I cannot stand,

From reading this thread and my own experiences, caffeine has been beneficial for me and others, but, obviously many people are very sensitive and can't tolerate it at all.
Caffeine has been proven to be effective in combo with OTC pain meds, like excedrin, tylenol and aspirin.
"Normal is just a cycle on a washing machine." "I don't have pet peeves I have whole kennels of irritation." --Whoopi Goldberg