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

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.

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.

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.

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.

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.

A hot cup of coffee or tea is a highlight of the morning for some people. It can make you feel awake and alert. Caffeine is the chemical that causes these sensations. But does caffeine have other effects on the brain?

Caffeine is found naturally in tea and coffee. But it is added to energy drinks and many types of soda. It’s even put in some snack foods and medications. More than eight out of 10 adults in the U.S. consume caffeine in some form.

So how does caffeine wake you up? Your body naturally produces a chemical called adenosine. It builds up in your body during the day.

“The sleepiness you feel at the end of the day—that’s adenosine,” explains Dr. Sergi Ferre, a brain scientist at NIH. Its buildup tells your brain when it’s time to rest.

Caffeine blocks adenosine from working on brain cells. This prevents you from feeling sleepy. “But the body adapts,” Ferre says. If you regularly consume caffeine, your body produces more adenosine. So people need more caffeine over time to get the same wakeful feeling.

Adenosine also makes it unpleasant to quit caffeine suddenly, says Ferre. If you take away the caffeine, extra adenosine in the body can cause feelings of withdrawal for a while. These include headaches and increased sleepiness.

Caffeine also interacts with other chemicals in the brain. If you consume more than normal, some of these interactions are what make you feel “overcaffeinated.” Your heart may race, or you can feel anxious or sick to your stomach.

But caffeine doesn’t affect everyone the same way. That’s because people’s bodies can break it down at different speeds. How fast your body does this depends largely on your genes , explains Dr. Marilyn Cornelis, a nutrition researcher at Northwestern University.

Experts recommend that some people avoid caffeine. These include people with gut troubles like acid reflux, people who have trouble sleeping, and people who have high blood pressure or heart problems. Children, teens, and women who are pregnant or breastfeeding are often advised to stay away from caffeine, too. Talk with your health care provider if you’re concerned about caffeine and your health.

“Even healthy people should avoid mixing caffeine with alcohol,” explains Ferre. “This is because caffeine can block the brain from feeling the depressant effects of alcohol. This might lead someone to drink more than they normally would, increasing their impairment.”

But research suggests that caffeine on its own is likely harmless for most healthy adults in low to moderate amounts, says Cornelis. She and others are studying whether it might even have positive effects on thinking, learning, and memory.

“When you drink caffeine, your attention is greater,” she says. “That contributes to our brain’s ability to retain information. That might lead to improvements in long-term cognitive function.” Her team is exploring new ways to measure the effects of caffeine on the brain and the role genes play in your body’s response.

While a few cups of unsweetened coffee or tea a day are likely fine for most people, Cornelis adds, some sources of caffeine can contain a lot of sugar. Excess sugar isn’t good for the body or brain, she says. If you’re looking for a pickup without sugar or caffeine, see the Wise Choices box for tips.

Stay Alert Without Caffeine

• Get enough sleep. Most adults need between seven and eight hours of sleep every night to feel rested.
• Eat regularly. When you don’t eat, your blood sugar levels drop, making you feel tired.
• Drink enough water. Staying hydrated can help you stay alert.
• Take a break for exercise. If you’re feeling drained in the middle of the day, it helps to move around.

Do you drink just one cup of coffee or tea first thing in the morning, hoping the caffeine in it will jump-start your day? Do you follow it up with a caffeinated beverage or two and then drink several more cups of coffee throughout the day?

Does it matter?

According to scientists at the FDA, caffeine can be part of a healthy diet for most people, but too much caffeine may pose a danger to your health. Depending on factors such as body weight, medications you may take, and individual sensitivity, “too much” can vary from person to person.

Learn more about caffeine in the following questions and answers.

1. Which kinds of foods and beverages contain caffeine?

Caffeine can be found naturally in the plants we use to make coffee, tea and chocolate. It’s also found in some plants used as flavorings, such as guarana, or alternative teas popular in South American, such as yerba mate (Ilex paraguariensis) and Ilex guayusa.

Caffeine may also be added as an ingredient to foods and beverages.

2. How do you know how much caffeine a food or beverage contains?

Many packaged foods, including beverages and dietary supplements containing caffeine, voluntarily provide information on the label as to how much caffeine they contain. Consumers should take care when consuming for the first time a new packaged food containing added caffeine if the amount of caffeine in the food is not declared on the label.

There are several online databases that provide estimates of caffeine content of certain foods and beverages such as coffee and tea. However, the amount in these brewed beverages can vary depending on such factors as how and where the coffee beans and tea leaves were grown and processed and how the beverage product is prepared.

For reference, a 12 ounce can of a caffeinated soft drink typically contains 30 to 40 milligrams of caffeine, an 8-ounce cup of green or black tea 30-50 milligrams, and an 8-ounce cup of coffee closer to 80 to 100 milligrams. Caffeine in energy drinks can range from 40-250 mg per 8 fluid ounces.

3. If a coffee or tea says “decaffeinated,” does that mean it contains no caffeine?

No. Decaf coffees and teas have less caffeine than their regular counterparts, but they still contain some caffeine. For example, decaf coffee typically has 2-15 milligrams in an 8-ounce cup. If you react strongly to caffeine in a negative way, you may want to avoid these beverages altogether.

4. How much caffeine is too much?

For healthy adults, the FDA has cited 400 milligrams a day—that's about four or five cups of coffee—as an amount not generally associated with dangerous, negative effects. However, there is wide variation in both how sensitive people are to the effects of caffeine and how fast they metabolize it (break it down).

Certain conditions tend to make people more sensitive to caffeine’s effects, as can some medications. In addition, if you’re pregnant, trying to become pregnant, or breastfeeding, or are concerned about another condition or medication, we recommend talking to your health care provider about whether you need to limit caffeine consumption.

The FDA has not set a level for children, but the American Academy of Pediatrics discourages the consumption of caffeine and other stimulants by children and adolescents.

5. How do you know if you’ve consumed more caffeine than you can tolerate?

Over-consuming caffeine can cause:

• insomnia
• jitters
• anxiousness
• fast heart rate
• upset stomach
• nausea
• headache
• a feeling of unhappiness (dysphoria)

6. Does caffeine pose a danger to your health?

The FDA estimates toxic effects, like seizures, can be observed with rapid consumption of around 1,200 milligrams of caffeine, or 0.15 tablespoons of pure caffeine.

Pure and highly concentrated caffeine products present a significant public health threat and have contributed to at least two deaths in the United States in the last few years. (In April, the FDA took action to protect consumers from these products.)

These products, often labeled as dietary supplements, consist of pure or highly concentrated caffeine in powder or liquid forms and are often marketed in bulk packaging with up to thousands of servings per container, requiring the consumer to measure out a safe serving from what can be a toxic or even lethal amount of bulk product.

The risk of caffeine overdose increases as the concentration of caffeine in the product increases, meaning even small dosages of a highly concentrated product could lead to dangerous effects. Just one teaspoon of pure powdered caffeine can contain the same amount of caffeine as 28 cups of coffee, and a half cup of a liquid highly concentrated caffeine product contains the equivalent of more than 20 cups of coffee. These are toxic amounts that can have serious health consequences, including death.

7. Is it okay for kids to consume caffeine?

We recommend you consult with your health care provider for advice regarding your child’s caffeine consumption.

8. Is drinking a lot of caffeine a substitute for sleep?

No. Caffeine is a stimulant, which may cause you to be more alert and awake, but it is not a substitute for sleep. Typically, it can take 4 to 6 hours for your body to metabolize half of what you consumed. So, a cup of coffee at dinner may keep you awake at bedtime.

9. How can I cut back on caffeine without causing unpleasant side effects?

If you’re used to drinking caffeine-containing beverages every day, and want to cut back, it’s best to do so gradually. Stopping abruptly can cause withdrawal symptoms such as headaches, anxiety, and nervousness. Unlike opioid or alcohol withdrawal, caffeine withdrawal is not considered dangerous, but it can be unpleasant. You may want to talk to your health care provider about how to cut back.

Most adults in the U.S. use caffeine, whether in coffee, soda, energy drinks, or chocolate. Many are also familiar with the effects of suddenly drinking less coffee than usual: tiredness, headaches, insomnia, and other symptoms. And many people talk about being “addicted” to their morning coffee or energy drink! But is caffeine truly addictive?

It’s all about the dopamine

The world’s caffeine obsession can be described as a “dependency” (because when you have less of it, you go through a mild “withdrawal,” with the symptoms listed above), but it is not an addiction.

It is true that—like many drugs—caffeine enhances dopamine signaling in the brain. Dopamine is a chemical that helps control movement, motivation, and emotions, so enhanced dopamine signaling makes a person feel more awake and alert. Because caffeine produces that alert feeling, it’s classified as a stimulant.

But wait—some prescription drugs and the dangerous drug methamphetamine (“meth”) and MDMA (ecstasy or Molly) are also types of stimulants. So what’s the difference?

While caffeine produces a small rise in dopamine, it does not cause the large surge that unbalances the reward circuits in the brain and is necessary for an addiction. So even though the word “addiction” is often used casually, caffeine is not addictive (scientifically speaking).

How do you define addiction?

NIDA defines addiction as the uncontrolled (or “compulsive”) use of a substance even when it causes negative consequences for the person using it. Dr. Nora Volkow, NIDA’s director, recently talked to Voice of America about the real definition of addiction.

So the difference between caffeine dependence and addiction to drugs like meth is that even a person who loves to drink coffee can do without it, deal with the headaches and irritability that result, and not engage in destructive (or self-destructive) behavior.

Too much caffeine—like too much anything—can still be harmful. But even if you just gotta have that energy drink, know that your love of caffeine doesn’t compare to a real drug addiction that can change your life forever, in very bad ways.