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. 

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Effects of caffeine

Caffeine 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; and
  • amount of regular consumption. 

Short term effects

Because caffeine is a stimulant, it is common to experience:

  • increased alertness
  • increased blood pressure
  • increased breathing rate 
  • increased urination

These 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 effects

Long-term use can lead to:

  • nervousness
  • insomnia
  • dehydration
  • stomach irritation
  • fatigue

Caffeine content

The 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:

Beverages Serving size (oz) Caffeine amount (mg)
Brewed coffee 8 80-115
Espresso 2 80
Cappuccino 8 80
Iced tea 8 30
Chocolate milk 8 5
Hot cocoa 8 6
Cola drinks 12 38-46
Jolt  12 70


Signs for Concern

Moderate 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 irritable
  • gastrointestinal aches
  • frequent urination
  • headaches
  • muscle tremors
  • difficulty falling asleep

Tips for Moderating Use

If 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 drink
  • Gradually lower your consumption by one cup at a time
  • Mix regular coffee with decaf / brew weaker tea
  • Opt for a non-caffeinated drink 
  • Get some more sleep / Take a nap, when tired
  • Exercise for an energy burst