Caffeine is a central nervous system stimulant and the most commonly consumed legal, psychoactive substance. It has a wide range of effects of most people and is considered safe in limited amounts. Learn more about:Effects of caffeineCaffeine contentSigns for concernTips for moderating useEffects of caffeineCaffeine takes about an hour to take affect (less on an empty stomach), and can lasts 4-6 hours. The actual effects of caffeine depend on a number of factors, including:genetics;body weight;medications being taken;health conditions; andamount of regular consumption. Short term effectsBecause caffeine is a stimulant, it is common to experience:increased alertnessincreased blood pressureincreased breathing rateincreased urinationThese effects are mostly due to caffeine increasing your metabolic rate (though it has not been linked to weight loss). Caffeine is also a diuretic, which causes increased urination, and may lead to dehydration. Long-term effectsLong-term use can lead to:nervousnessinsomniadehydrationstomach irritationfatigueCaffeine contentThe amount of caffeine in a drink depends on the size and the chemical components. Here is a list of common drinks, their size and caffeine content:BeveragesServing size (oz)Caffeine amount (mg)Brewed coffee880-115Espresso280Cappuccino880Iced tea830Chocolate milk85Hot cocoa86Cola drinks1238-46Jolt 1270Signs for ConcernModerate caffeine use (400 milligrams or 4 cups a day) is considered safe for healthy adults. However, you may want to take a look at your intake if you experience any of these negative side effects:nervous, dizzy, or irritablegastrointestinal achesfrequent urinationheadachesmuscle tremorsdifficulty falling asleepTips for Moderating UseIf you drink two or more cups of a caffeinated drink each day, you will most likely experience withdrawal if you stop drinking it completely. The most common symptom of caffeine withdrawal is a headache, but you may also experience more severe effects, such as anxiety, fatigue, and depression. If you want to eliminate caffeine from your diet, it is best to reduce intake gradually.Some other tips for reducing caffeine use are to:Keep track of how much caffeine you drinkGradually lower your consumption by one cup at a timeMix regular coffee with decaf / brew weaker teaOpt for a non-caffeinated drinkGet some more sleep / Take a nap, when tiredExercise for an energy burst