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What is caffeine?

Caffeine is a stimulant that affects the central nervous system (CNS) found in coffee, tea, chocolate and some energy drinks. Caffeine may increase alertness and help individuals stay awake however, it may also increase heart rate, dehydration, cause insomnia or restlessness as well as contribute to headaches. 

Is caffeine bad for you?

While caffeine was once considered bad for you, it is now generally considered safe. In fact, some nutritionists would even describe it as ‘healthy’. In truth, it can have both positive and negative impacts on your overall health. 

On the positive side, caffeine can give you a sense of awareness and focus which may be necessary to tackle a particularly monotonous task. Because of how it affects your brain, caffeine may improve the mood and brain function of some people. Some studies have linked caffeine to weight loss and improved sports performance. 

However, well-known side effects from excessive caffeine consumption include anxiety, restlessness, tremors, irregular heartbeat, and trouble sleeping. It can also cause headaches, migraines, and high blood pressure. 

Is caffeine a drug?

Caffeine is widely considered a stimulant and psychoactive drug because of its effects on brain function. 

When caffeine is consumed, it blocks a molecule called adenosine and prevents you from feeling tired. It may also increase blood flow to the brain and increase the activity of two other neurotransmitters called dopamine and norepinephrine. 

How long do the effects of caffeine last?

Generally speaking, the effects of caffeine last around six to eight hours. When you first consume caffeine, it begins to take effect within 20 or so minutes and reaches its maximum impact after about an hour. It can take up to 10 hours to completely clear caffeine from your system. 

What is caffeine withdrawal?

Caffeine withdrawal is a term used to describe symptoms experienced by people who regularly consume caffeine and suddenly quit. Common caffeine withdrawal symptoms include headaches, fatigue, changes in your mood, and difficulty concentrating.

How much caffeine is in a cup of coffee?

The amount of caffeine found in a cup of coffee depends on the bean, roast, and how much water is filtered through the grinds. An 8-ounce cup of coffee contains approximately 102–200 mg of caffeine.

How much caffeine is in tea?

Like coffee, the amount of caffeine in tea will vary depending on the type of tea, how long it steeps, and how much water is in the cup. An 8-ounce cup of brewed black tea contains approximately 40–120 mg of caffeine while an 8-ounce cup of brewed green tea contains approximately 30–60 mg.

Related Terms

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Photo of Kristin Ricklefs-Johnson

Medically reviewed by:

Kristin Ricklefs-Johnson, Ph.D., RD

Kristin is an RDN who also earned her Ph.D. in Nutrition from Arizona State University with an emphasis on insulin resistance, lipid metabolism disorders, and obesity. She completed her post-doctoral fellowship at Mayo Clinic where she focused on nutrition-related proteomic and metabolic research. Her interests include understanding the exact mechanism of action of various genetic variations underlying individual predispositions to nutrition-related health outcomes. Her goal is to help all individuals prevent chronic diseases and achieve long, healthy lives through eating well.

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