Coffee has the most caffeine. Tea has less and cola beverages the least. The amount in coffee and tea varies greatly depending on the specific brand and brewing method. This makes it hard to get the same amount each time. Cola beverages always contain the same amount and you can buy caffeine tablets at any pharmacy.
Some people maximize the drug effects by only consuming caffeine once a week.
This is useful for one day or night of very high energy levels. If you discontinue using it entirely you may get caffeine withdrawal headaches. Most people who drink five or more cups of coffee per day will have these headaches which can be as disabling as any migraine headache. Then use it like a drug to give you a physical and mental lift when you want it most.