What does caffeine do?

  • Acts as a stimulant, which keeps you awake and alert
  • Acts as a diuretic (a substance that helps your body get rid of extra salt and water by urinating more)
  • Increases how much acid your stomach releases, which can sometimes lead to heartburn or an upset stomach
  • May affect how well your body absorbs calcium from food
  • Raises blood pressure

What is a safe amount of caffeine?

  • Adults age 18 and older: 300-400 milligrams (mg) a day. That is about 4 cups of coffee, 10 cans of soda or two energy shot drinks a day.
  • Teens age 18 and under: 100 mg a day. This is about one cup of coffee or 2 cans of soda a day.

What are side effects of caffeine?

  • Poor sleep or insomnia (sleeplessness)
  • Restlessness or shakiness
  • Headaches or dizziness
  • Rapid or abnormal (unusual) heart beat
  • Dehydration
  • Anxiety
  • Dependency (when you have to drink more and more caffeine to feel the same effects)

It is best to cut back on caffeine slowly. If you stop suddenly or too quickly, you might feel unwell. You might also experience symptoms of caffeine withdrawal.

Symptoms of caffeine withdrawal include fatigue, headaches and depressed mood.

Amount of caffeine in your favorite drinks


  • Brewed coffee (8 ounces, oz.): 95-310 milligrams (mg)
    • Low: Dunkin Donuts® (medium): 210 mg
    • High: Startbucks® (grande): 310 mg
  • Brewed decaf coffee (8 oz.): 5 mg
  • Espresso (1 oz.): 50 mg
  • Latte or mocha (8 oz.): 60 mg


  • Brewed black (8 oz.): 30 mg
  • Brewed green (8 oz.): 20 mg
  • Bottled or ready-to-drink: Honest Tea® Organic Lemon (17 oz.): 90 mg


  • Citrus (8 oz.): 0 mg
  • Cola (8 oz.): 30 mg

Energy Drinks

  • Red Bull® (8 oz.): 80 mg
  • Monster® (16 oz.): 160 mg
  • Energy shot (1 oz.): 50 mg

How caffeine affects your sleep

You can feel the effects of caffeine within one hour of drinking a caffeinated drink. You can continue to feel the effects for 4-6 hours.

To help you sleep better, try the following:

  • Stop drinking caffeinated drinks 4-6 hours before bed.
  • Try drinking half caffeinated and half decaffeinated coffee or tea.
  • Lessen how much caffeine you have slowly. Try cutting down one serving per day.

A note about enery drinks...

Energy drinks have a lot of caffeine added to them. They can be dangerous. Companies claim they can increase alertness and mental and physical performance. There is very little research showing that energy drinks might do this for a short period of time.

Energy drinks also have lots of extra sugar. They can contribute to weight gain and diabetes.

Rev. 4/2019. Created by Judith Sharlin, PhD, RD. MassGeneral Hospital for Children and Massachusetts General Hospital do not endorse any of the brands listed on this handout. This handout is intended to provide health information so that you can be better informed. It is not a substitute for medical advice and should not be used to treatment of any medical conditions.