- Acute Flaccid Myelitis
- Alzheimer’s Disease
- Arteriovenous Malformations
- Attention Deficit Hyperactivity Disorder
- Back Pain
- Brain Aneurysm
- Brain Tumors
- Carpal Tunnel Syndrome
- Childhood Brain Tumors
- Delirium
- Dementia
- Hemorrhagic Stroke
- Ischemic Stroke
- Memory
- Meningitis
- Mild Cognitive Impairment
- Movement Disorders
- Multiple Sclerosis
- Neuroblastoma
- Neuromuscular Disorders
- Parkinson’s Disease
- Polio and Post-Polio Syndrome
- Speech and Language Problems in Children
- Stroke
- Transient Ischemic Attack
- Tremor
- Walking Problems
- West Nile Virus
- A1C
- Blood Glucose
- Diabetes
- Diabetes and Pregnancy
- Diabetes Complications
- Diabetes in Children and Teens
- Diabetes Medicines
- Diabetes Type 1
- Diabetes Type 2
- Diabetic Diet
- Diabetic Eye Problems
- Diabetic Foot
- Diabetic Heart Disease
- Diabetic Kidney Problems
- Diabetic Nerve Problems
- How to Prevent Diabetes
- Hyperglycemia
- Metabolic Syndrome
- Prediabetes
- Abortion
- Breast Cancer
- Breast Diseases
- Breast Reconstruction
- Breastfeeding
- Cervical Cancer
- Cervical Cancer Screening
- Cesarean Delivery
- Childbirth
- Ectopic Pregnancy
- Endometriosis
- Female Infertility
- Health Problems in Pregnancy
- High Blood Pressure in Pregnancy
- HIV and Pregnancy
- Hormone Replacement Therapy
- HPV
- Hysterectomy
- Infections and Pregnancy
- Mammography
- Mastectomy
- Menopause
- Menstruation
- Miscarriage
- Ovarian Cancer
- Ovarian Cysts
- Ovarian Disorders
- Pelvic Floor Disorders
- Pelvic Inflammatory Disease
- Pelvic Pain
- Period Pain
- Polycystic Ovary Syndrome
- Pregnancy
- Pregnancy and Drug Use
- Pregnancy and Opioids
- Premenstrual Syndrome
- Prenatal Care
- Prenatal Testing
- Primary Ovarian Insufficiency
- Sexual Problems in Women
- Stillbirth
- Teenage Pregnancy
- Trichomoniasis
- Tubal Ligation
- Uterine Cancer
- Uterine Diseases
- Uterine Fibroids
- Vaginal Bleeding
- Vaginal Cancer
- Vaginal Diseases
- Vaginitis
- Vulvar Cancer
- Vulvar Disorders
- Yeast Infections
- Alcohol
- Calcium
- Child Nutrition
- Cholesterol
- Cholesterol Levels: What You Need to Know
- Cholesterol Medicines
- DASH Eating Plan
- Eating Disorders
- Food Allergy
- HDL: The “Good” Cholesterol
- High Cholesterol in Children and Teens
- How to Lower Cholesterol
- How to Lower Cholesterol with Diet
- Infant and Newborn Nutrition
- LDL: The “Bad” Cholesterol
- Malabsorption Syndromes
- Nutrition for Older Adults
- Pregnancy and Nutrition
- Toddler Nutrition
- Triglycerides
- VLDL Cholesterol
- Alpha-1 Antitrypsin Deficiency
- Ataxia Telangiectasia
- Brain Malformations
- Cerebral Palsy
- Charcot-Marie-Tooth Disease
- Chiari Malformation
- Cleft Lip and Palate
- Color Blindness
- Congenital Heart Defects
- Craniofacial Abnormalities
- Cystic Fibrosis
- Ehlers-Danlos Syndrome
- Fetal Alcohol Spectrum Disorders
- Friedreich Ataxia
- Genetic Counseling
- Hemophilia
- Huntington’s Disease
- Hydrocephalus
- Muscular Dystrophy
- Neural Tube Defects
- Neurofibromatosis
- Newborn Screening
- Osteogenesis Imperfecta
- Prader-Willi Syndrome
- Pregnancy and Medicines
- Rett Syndrome
- Sickle Cell Disease
- Spina Bifida
- Spinal Muscular Atrophy
- Tay-Sachs Disease
- Tourette Syndrome
- Tuberous Sclerosis
- Usher Syndrome
- Acute Lymphocytic Leukemia
- Allergy
- Animal Bites
- Ankylosing Spondylitis
- Aplastic Anemia
- Asthma
- Asthma in Children
- Childhood Leukemia
- Childhood Vaccines
- Chronic Lymphocytic Leukemia
- COVID-19 Vaccines
- Cryptosporidiosis
- Eosinophilic Disorders
- Eosinophilic Esophagitis
- Giant Cell Arteritis
- Hay Fever
- HIV
- HIV and Infections
- HIV in Women
- Hodgkin Lymphoma
- Infectious Diseases
- Infectious Mononucleosis
- Juvenile Arthritis
- Kawasaki Disease
- Lymphedema
- Lymphoma
- Multiple Myeloma
- Pemphigus
- Pneumocystis Infections
- Rheumatoid Arthritis
- Scleroderma
- Sjogren’s Syndrome
- Tonsillitis
- Vaccines
- Viral Infections
- Adhesions
- Ankle Injuries and Disorders
- Arm Injuries and Disorders
- Back Injuries
- Brachial Plexus Injuries
- Burns
- Chest Injuries and Disorders
- Concussion
- CPR
- Dislocated Shoulder
- Dislocations
- Elbow Injuries and Disorders
- Eye Injuries
- Facial Injuries and Disorders
- Finger Injuries and Disorders
- Foot Injuries and Disorders
- Fractures
- Hand Injuries and Disorders
- Heel Injuries and Disorders
- Hip Injuries and Disorders
- Inhalation Injuries
- Insect Bites and Stings
- Jaw Injuries and Disorders
- Knee Injuries and Disorders
- Leg Injuries and Disorders
- Mosquito Bites
- Neck Injuries and Disorders
- Rotator Cuff Injuries
- Shoulder Injuries and Disorders
- Spinal Cord Injuries
- Sprains and Strains
- Tick Bites
- Toe Injuries and Disorders
- Traumatic Brain Injury
- Wrist Injuries and Disorders
- Acute Bronchitis
- Bird Flu
- Chronic Bronchitis
- COPD
- COVID-19 (Coronavirus Disease 2019)
- Croup
- E-Cigarettes
- Fistulas
- Flu
- Granulomatosis with Polyangiitis
- H1N1 Flu (Swine Flu)
- Legionnaires’ Disease
- Lung Cancer
- Mesothelioma
- Pneumonia
- Pulmonary Hypertension
- Respiratory Syncytial Virus Infections
- Sleep Apnea
- Smoking
- Tuberculosis
- Whooping Cough
- Anatomy
- Assisted Reproductive Technology
- Birth Control
- Chlamydia Infections
- Circumcision
- Erectile Dysfunction
- Genital Herpes
- Genital Warts
- Gonorrhea
- Herpes Simplex
- Infertility
- Male Infertility
- Penis Disorders
- Prostate Cancer
- Prostate Cancer Screening
- Prostate Diseases
- Reproductive Hazards
- Sexual Health
- Sexual Problems in Men
- Sexually Transmitted Diseases
- Syphilis
- Testicular Cancer
- Testicular Disorders
- Vasectomy
- Abdominal Pain
- Bad Breath
- Bleeding
- Breathing Problems
- Bruises
- Chest Pain
- Choking
- Chronic Pain
- Constipation
- Cough
- Diarrhea
- Dizziness and Vertigo
- Edema
- Fainting
- Fever
- Frostbite
- Gas
- Gastrointestinal Bleeding
- Headache
- Heartburn
- Heat Illness
- Hives
- Hypothermia
- Indigestion
- Itching
- Jaundice
- Nausea and Vomiting
- Pain
- Rare Diseases
- Raynaud’s Disease
- Sciatica
- Speech and Communication Disorders
- Stuttering
Caffeine
Summary
What is caffeine?
Caffeine is a bitter substance that occurs naturally in more than 60 plants including:
- Coffee beans
- Tea leaves
- Kola nuts, which are used to flavor soft drink colas
- Cacao pods, which are used to make chocolate products
There is also synthetic (man-made) caffeine, which is added to some medicines, foods, and drinks. For example, some pain relievers, cold medicines, and over-the-counter medicines for alertness contain synthetic caffeine. So do energy drinks and “energy-boosting” gums and snacks.
Most people consume caffeine from drinks. The amount of caffeine in different drinks can vary a lot, but it is generally:
- An 8-ounce cup of coffee: 95-200 mg
- A 12-ounce can of cola: 35-45 mg
- An 8-ounce energy drink: 70-100 mg
- An 8-ounce cup of tea: 14-60 mg
What are caffeine’s effects on the body?
Caffeine has many effects on your body’s metabolism. It:
- Stimulates your central nervous system, which can make you feel more awake and give you a boost of energy
- Is a diuretic, meaning that it helps your body get rid of extra salt and water by urinating more
- Increases the release of acid in your stomach, sometimes leading to an upset stomach or heartburn
- May interfere with the absorption of calcium in the body
- Increases your blood pressure
Within one hour of eating or drinking caffeine, it reaches its peak level in your blood. You may continue to feel the effects of caffeine for four to six hours.
What are the side effects from too much caffeine?
For most people, it is not harmful to consume up to 400mg of caffeine a day. If you do eat or drink too much caffeine, it can cause health problems, such as:
- Restlessness and shakiness
- Insomnia
- Headaches
- Dizziness
- Fast heart rate
- Dehydration
- Anxiety
- Dependency, so you need to take more of it to get the same results
Some people are more sensitive to the effects of caffeine than others.
What are energy drinks, and why can they be a problem?
Energy drinks are beverages that have added caffeine. The amount of caffeine in energy drinks can vary widely, and sometimes the labels on the drinks do not give you the actual amount of caffeine in them. Energy drinks may also contain sugars, vitamins, herbs, and supplements.
Companies that make energy drinks claim that the drinks can increase alertness and improve physical and mental performance. This has helped make the drinks popular with American teens and young adults. There’s limited data showing that energy drinks might temporarily improve alertness and physical endurance. There is not enough evidence to show that they enhance strength or power. But what we do know is that energy drinks can be dangerous because they have large amounts of caffeine. And since they have lots of sugar, they can contribute to weight gain and worsen diabetes.
Sometimes young people mix their energy drinks with alcohol. It is dangerous to combine alcohol and caffeine. Caffeine can interfere with your ability to recognize how drunk you are, which can lead you to drink more. This also makes you more likely to make bad decisions.
Who should avoid or limit caffeine?
You should check with your health care provider about whether you should limit or avoid caffeine if you:
- Are pregnant, since caffeine passes through the placenta to your baby.
- Are breastfeeding, since a small amount of caffeine that you consume is passed along to your baby.
- Have sleep disorders, including insomnia.
- Have migraines or other chronic headaches.
- Have anxiety.
- Have GERD or ulcers.
- Have arrhythmia (a problem with the rate or rhythm of your heartbeat).
- Have high blood pressure.
- Take certain medicines or supplements, including stimulants, certain antibiotics, asthma medicines, and heart medicines. Check with your health care provider about whether there might be interactions between caffeine and any medicines and supplements that you take.
- Are a child or teen. Neither should have as much caffeine as adults. Children can be especially sensitive to the effects of caffeine.
What is caffeine withdrawal?
If you have been consuming caffeine on a regular basis and then suddenly stop, you may have caffeine withdrawal. Symptoms can include:
- Headaches
- Drowsiness
- Irritability
- Nausea
- Trouble concentrating
These symptoms usually go away after a couple of days.
Related Issues
- Alcohol and Caffeine Centers for Disease Control and Prevention
- Benefits of Coffee Academy of Nutrition and Dietetics
- Caffeine and Migraine American Migraine Foundation
- Caffeine: How Does It Affect Blood Pressure? Mayo Foundation for Medical Education and Research
- Truth about Energy Drinks American Academy of Family Physicians
Children
- Caffeine (For Parents) Nemours Foundation
Women
- Caffeine in Pregnancy Organization of Teratology Information Specialists
Patient Handouts
- Caffeine in the diet Medical Encyclopedia
- Caffeine overdose Medical Encyclopedia
Start Here
- Caffeine: How Much Is Too Much? Mayo Foundation for Medical Education and Research
- Nutrition and Healthy Eating: Caffeine Mayo Foundation for Medical Education and Research
- Spilling the Beans: How Much Caffeine is Too Much? Food and Drug Administration
- Tired or Wired? Caffeine and Your Brain National Institutes of Health
Clinical Trials
- ClinicalTrials.gov: Caffeine National Institutes of Health
Find an Expert
- National Institute of Environmental Health Sciences National Institute of Environmental Health Sciences