Caffeine is a bitter substance found in coffee, tea, soft drinks, chocolate, kola nuts, and certain medicines. It has many effects on the body's metabolism, including stimulating the central nervous system. This can make you more alert and give you a boost of energy.
For most people, the amount of caffeine in two to four cups of coffee a day is not harmful. However, too much caffeine can cause problems. It can
- Make you jittery and shaky
- Make it hard to fall asleep or stay asleep
- Cause headaches or dizziness
- Make your heart beat faster or cause abnormal heart rhythms
- Cause dehydration
- Make you dependent on it so you need to take more of it. If you stop using caffeine, you could get withdrawal symptoms.
Some people are more sensitive to the effects of caffeine than others. They should limit their use of caffeine. So should pregnant and nursing women. Certain drugs and supplements may interact with caffeine. If you have questions about whether caffeine is safe for you, talk with your health care provider.
Food and Drug Administration
- Benefits of Java (Academy of Nutrition and Dietetics)
- Caffeine and Alcohol (Centers for Disease Control and Prevention)
- Caffeine and Heart Disease (American Heart Association)
- Caffeine and Migraine (American Migraine Foundation)
- Caffeine: Can It Help Me Lose Weight? (Mayo Foundation for Medical Education and Research)
- Caffeine: How Does It Affect Blood Pressure? (Mayo Foundation for Medical Education and Research)
- Energy Drinks (National Center for Complementary and Integrative Health)
- Serious Concerns Over Alcoholic Beverages with Added Caffeine (Food and Drug Administration)
- Truth About Energy Drinks (American Academy of Family Physicians)
Statistics and Research
- Update on Emergency Department Visits Involving Energy Drinks: A Continuing Public Health Concern (Substance Abuse and Mental Health Services Administration)
- ClinicalTrials.gov: Caffeine (National Institutes of Health)
Journal ArticlesReferences and abstracts from MEDLINE/PubMed (National Library of Medicine)
- Article: Effects of caffeine on endurance capacity and psychological state in...
- Article: Effects of caffeine on neuromuscular fatigue and performance during high-intensity...
- Article: Acute Low-Dose Caffeine Supplementation Increases Electromyographic Fatigue Threshold in Healthy...
- Caffeine -- see more articles