arrhythmias

An arrhythmia is a problem with the rate or rhythm of your heartbeat. It means that your heart beats too quickly, too slowly, or with an irregular pattern. When the heart beats faster than normal, it is called tachycardia. When the heart beats too slowly, it is called bradycardia. The most common type of arrhythmia is atrial fibrillation, which causes an irregular and fast heart beat.

Many factors can affect your heart's rhythm, such as having had a heart attack, smoking, congenital heart defects, and stress. Some substances or medicines may also cause arrhythmias.

Symptoms of arrhythmias include:

• Fast or slow heart beat
• Skipping beats
• Lightheadedness or dizziness
• Chest pain
• Shortness of breath
• Sweating

Your doctor can run tests to find out if you have an arrhythmia. Treatment to restore a normal heart rhythm may include medicines, an implantable cardioverter-defibrillator (ICD) or pacemaker, or sometimes surgery.

NIH: National Heart, Lung, and Blood Institute

Sudden cardiac arrest (SCA) is a condition in which the heart suddenly stops beating. When that happens, blood stops flowing to the brain and other vital organs. If it is not treated, SCA usually causes death within minutes. But quick treatment with a defibrillator may be lifesaving.

A heart attack is different from an SCA. A heart attack happens when blood flow to the heart is blocked. During a heart attack, the heart usually doesn't suddenly stop beating. With an SCA, the heart stops beating.

Sometimes an SCA can happen after or during recovery from a heart attack.

Your heart has an electrical system that controls the rate and rhythm of your heartbeat. An SCA can happen when the heart's electrical system is not working right and causes irregular heartbeats. Irregular heartbeats are called arrhythmias. There are different types. They may cause the heart to beat too fast, too slow, or with an irregular rhythm. Some can cause the heart to stop pumping blood to the body; this is the type that causes SCA.

Certain diseases and conditions can cause the electrical problems that lead to SCA. They include:

• Ventricular fibrillation, a type of arrhythmia where the ventricles (the heart's lower chambers) don't beat normally. Instead, they beat very fast and very irregularly. They can't pump blood to the body. This causes most SCAs.
• Coronary artery disease (CAD), also called ischemic heart disease. CAD happens when the arteries of the heart cannot deliver enough oxygen-rich blood to the heart. It is often caused by the buildup of plaque, a waxy substance, inside the lining of larger coronary arteries. The plaque blocks some or all of the blood flow to the heart.
• Some types of physical stress can cause your heart's electrical system to fail, such as
  • Intense physical activity in which your body releases the hormone adrenaline. This hormone can trigger SCA in people who have heart problems.
  • Very low blood levels of potassium or magnesium. These minerals play an important role in your heart's electrical system.
  • Major blood loss
  • Severe lack of oxygen
• Certain inherited disorders which can cause arrhythmias or problems with the structure of your heart
• Structural changes in the heart, such as an enlarged heart due to high blood pressure or advanced heart disease. Heart infections can also cause changes to the structure of the heart.

You are at higher risk for SCA if you:

• Have coronary artery disease (CAD). Most people with SCA have CAD. But CAD usually doesn't cause symptoms, so they may not know that they have it.
• Are older; your risk increases with age
• Are a man; it is more common in men than women
• Are Black or African American, especially if you have other conditions such as diabetes, high blood pressure, heart failure, or chronic kidney disease
• Have a personal history of heartbeats that aren't regular (arrhythmia)
• Have a personal or family history of SCA or inherited disorders that can cause arrhythmia
• Have a problem with drug or alcohol use
• Have had a heart attack
• Have heart failure

Usually, the first sign of SCA is loss of consciousness (fainting). This happens when the heart stops beating.

Some people may have a racing heartbeat or feel dizzy or light-headed just before they faint. And sometimes people have chest pain, shortness of breath, nausea, or vomiting in the hour before they have an SCA.

SCA happens without warning and requires emergency treatment. Health care providers rarely diagnose SCA with medical tests as it's happening. Instead, it is usually diagnosed after it happens. Providers do this by ruling out other causes of a person's sudden collapse.

If you are at high risk for SCA, your provider may refer you to a cardiologist, a doctor who specializes in heart diseases. The cardiologist may ask you to get various heart health tests to see how well you heart is working. He or she will work with you to decide whether you need treatment to prevent SCA.

SCA is an emergency. A person having SCA needs to be treated with a defibrillator right away. A defibrillator is a device sends an electric shock to the heart. The electric shock can restore a normal rhythm to a heart that's stopped beating. To work well, it needs to be done within minutes of the SCA.

Most police officers, emergency medical technicians, and other first responders are trained and equipped to use a defibrillator. Call 9-1-1 right away if someone has signs or symptoms of SCA. The sooner you call for help, the sooner lifesaving treatment can begin.

Many public places such as schools, businesses, and airports have automated external defibrillators (AEDs). AEDs are special defibrillators that untrained people can use if they think that someone has had SCA. AEDS are programmed to give an electric shock if they detect a dangerous arrhythmia. This prevents giving a shock to someone who may have fainted but isn't having SCA.

If you see someone who you think has had SCA, you should give cardiopulmonary resuscitation (CPR) until defibrillation can be done.

People who are at risk for SCA may want to consider having an AED at home. Ask your cardiologist to help you decide whether having an AED in your home might help you.

If you survive SCA, you'll likely be admitted to a hospital for ongoing care and treatment. In the hospital, your medical team will closely watch your heart. They may give you medicines to try to reduce the risk of another SCA.

They will also try to find out what caused your SCA. If you're diagnosed with coronary artery disease, you may have an angioplasty or coronary artery bypass surgery. These procedures help restore blood flow through narrowed or blocked coronary arteries.

Often, people who have had SCA get a device called an implantable cardioverter defibrillator (ICD). This small device is surgically placed under the skin in your chest or abdomen. An ICD uses electric pulses or shocks to help control dangerous arrhythmias.

You may be able to lower your risk of SCA by following a heart-healthy lifestyle. If you have coronary artery disease or another heart disease, treating that disease can also lower your risk of SCA. If you have had an SCA, getting an implantable cardioverter defibrillator (ICD) can lower your chance of having another SCA.

NIH: National Heart, Lung, and Blood Institute

Atrial fibrillation, also known as AFib or AF, is one of the most common types of arrhythmias. Arrhythmias are problems with the rate or rhythm of your heartbeat. They can cause your heart to beat too slowly, too fast, or in an irregular way.

If you have AFib, your heart beats irregularly and sometimes much faster than normal. Also, your heart's upper and lower chambers do not work together as they should. When this happens, the lower chambers do not fill completely or pump enough blood to your lungs and body. This can cause symptoms such as dizziness, fatigue, and a pounding heartbeat.

AFib may happen in brief episodes, or it may be a permanent condition. It's very important to treat it, since AFib can put you at risk for stroke and other heart conditions.

AFib is most often caused by changes to the heart's tissue or the electrical signaling that helps the heartbeat. These changes can happen due to different conditions and factors, such as high blood pressure, coronary artery disease, congenital heart defects, infections, and aging. Sometimes the cause is unknown.

Anyone can develop AFib, but there are certain things that raise your risk for it:

• Aging. The risk of atrial fibrillation increases as you get older, especially when you are over age 65.
• Family history and genetics. AFib can run in families. So can heart disease, which raises your risk of AFib.
• Some lifestyle choices. Your risk is higher if you drink a lot of alcohol, use certain illegal drugs such as cocaine and methamphetamines, or smoke.
• Having certain health conditions, such as:
  • High blood pressure
  • Diabetes
  • Heart failure
  • Heart valve diseases
  • Obesity
  • Hyperthyroidism
  • Chronic kidney disease
  • COPD and other lung diseases
  • Sleep apnea
• Race. AFib is more common in people with European ancestry.
• Recent surgery. You may be at risk of atrial fibrillation in the early days and weeks after surgery on your heart, lungs, or esophagus.

Some people who have AFib don't have any symptoms and don't know they have it. If you do have symptoms, you may only notice them once in a while. Or you may have symptoms that are more frequent. And in some cases, the symptoms might be severe. If you have heart disease, you are more likely to notice your symptoms. And those symptoms could get worse if your heart disease gets worse.

The symptoms of AFib can include:

• Extreme fatigue, which is the most common symptom
• Heart palpitations (the feeling that your heart is skipping a beat, fluttering, pounding, or beating too hard or too fast)
• Trouble breathing, especially when lying down or when exercising
• Chest pain
• Dizziness or fainting
• Low blood pressure

If AFib is not treated, it can lead to serious health problems (complications) such as:

• Stroke
• Heart failure
• Blood clots
• Sudden cardiac arrest (SCA)
• Cognitive impairment and dementia

To help prevent these problems, it's important to contact your health care provider if you are having symptoms. If you do have AFib, the sooner you are diagnosed and treated, the better.

To find out if you have AFib, your provider:

• Will ask about your medical history, including your symptoms, lifestyle, and any other health conditions you may have
• Will ask about your family history, to find out if you have relatives who have or had AFib
• Will do a physical exam
• May order blood tests
• Will likely order heart tests, such as an electrocardiogram (also called an EKG or ECG) and echocardiogram
• May ask you to wear a heart monitor device that records your heart's electrical activity

The treatments for AFib may include:

• Blood thinner medicines that help prevent blood clots from forming.
• Medicines to control your heart's rhythm and rate.
• Following heart-healthy lifestyle changes, such as:
  • Following a heart-healthy eating plan that limits saturated fats, salt, and cholesterol. An example is the DASH eating plan.
  • Limiting or avoiding alcohol, because it can increase your heart rate.
  • Aiming for a healthy weight.
  • Getting regular physical activity.
  • Managing stress.
  • Quitting smoking.
• Procedures such as:
  • Electrical cardioversion, which restores your heart rhythm using low-energy shocks to your heart.
  • Catheter ablation, which scars the tissue that is causing the arrhythmia. The scar tissue blocks the abnormal heart signals.
• Surgeries such as:
  • Surgery to put in a pacemaker to help control the arrhythmia.
  • A Maze procedure, which creates scar tissue in a maze-like pattern in certain parts of the heart.
  • Left atrial appendage closure, a surgery on a small sac in the muscle wall of your left atrium (the upper left chamber of your heart). It helps prevent blood clots and can reduce your risk of stroke. This surgery is for people who are not able to take blood thinners.

There are steps you can take to help lower your risk of atrial fibrillation, such as:

• Making heart-healthy lifestyle changes:
  • Following a heart-healthy eating plan
  • Limiting or avoiding alcohol
  • Aiming for a healthy weight
  • Getting regular physical activity
  • Managing stress
  • Not smoking
• Avoiding illegal drugs, such as cocaine and methamphetamines
• Taking antiarrhythmic medicine (medicine to treat arrhythmia) if you are having heart surgery
• Treating any health conditions that could raise your risk of AFib

NIH: National Heart, Lung, and Blood Institute

An arrhythmia is any disorder of your heart rate or rhythm. It means that your heart beats too quickly, too slowly, or with an irregular pattern. Most arrhythmias result from problems in the electrical system of the heart. If your arrhythmia is serious, you may need a cardiac pacemaker or an implantable cardioverter defibrillator (ICD). They are devices that are implanted in your chest or abdomen.

A pacemaker helps control abnormal heart rhythms. It uses electrical pulses to prompt the heart to beat at a normal rate. It can speed up a slow heart rhythm, control a fast heart rhythm, and coordinate the chambers of the heart.

An ICD monitors heart rhythms. If it senses dangerous rhythms, it delivers shocks. This treatment is called defibrillation. An ICD can help control life-threatening arrhythmias, especially those that can cause sudden cardiac arrest (SCA). Most new ICDs can act as both a pacemaker and a defibrillator. Many ICDs also record the heart's electrical patterns when there is an abnormal heartbeat. This can help the doctor plan future treatment.

Getting a pacemaker or ICD requires minor surgery. You usually need to stay in the hospital for a day or two, so your doctor can make sure that the device is working well. You will probably be back to your normal activities within a few days.

Respiratory failure is a condition in which your blood doesn't have enough oxygen or has too much carbon dioxide. Sometimes you can have both problems.

When you breathe, your lungs take in oxygen. The oxygen passes into your blood, which carries it to your organs. Your organs, such as your heart and brain, need this oxygen-rich blood to work well.

Another part of breathing is removing the carbon dioxide from the blood and breathing it out. Having too much carbon dioxide in your blood can harm your organs.

Conditions that affect your breathing can cause respiratory failure. These conditions may affect the muscles, nerves, bones, or tissues that support breathing. Or they may affect the lungs directly. These conditions include:

• Diseases that affect the lungs, such as COPD (chronic obstructive pulmonary disease), cystic fibrosis, pneumonia, pulmonary embolism, and COVID-19
• Conditions that affect the nerves and muscles that control breathing, such as amyotrophic lateral sclerosis (ALS), muscular dystrophy, spinal cord injuries, and stroke
• Problems with the spine, such as scoliosis (a curve in the spine). They can affect the bones and muscles used for breathing.
• Damage to the tissues and ribs around the lungs. An injury to the chest can cause this damage.
• Drug or alcohol overdose
• Inhalation injuries, such as from inhaling smoke (from fires) or harmful fumes

The symptoms of respiratory failure depend on the cause and the levels of oxygen and carbon dioxide in your blood.

A low oxygen level in the blood can cause shortness of breath and air hunger (the feeling that you can't breathe in enough air). Your skin, lips, and fingernails may also have a bluish color. A high carbon dioxide level can cause rapid breathing and confusion.

Some people who have respiratory failure may become very sleepy or lose consciousness. They also may have arrhythmia (irregular heartbeat). You may have these symptoms if your brain and heart are not getting enough oxygen.

Your health care provider will diagnose respiratory failure based on:

• Your medical history
• A physical exam, which often includes
• Listening to your lungs to check for abnormal sounds
• Listening to your heart to check for arrhythmia
• Looking for a bluish color on your skin, lips, and fingernails
• Diagnostic tests, such as
• Pulse oximetry, a small sensor that uses a light to measure how much oxygen is in your blood. The sensor goes on the end of your finger or on your ear.
• Arterial blood gas test, a test that measures the oxygen and carbon dioxide levels in your blood. The blood sample is taken from an artery, usually in your wrist.

Once you are diagnosed with respiratory failure, your provider will look for what is causing it. Tests for this often include a chest x-ray. If your provider thinks you may have arrhythmia because of the respiratory failure, you may have an EKG (electrocardiogram). This is simple, painless test that detects and records your heart's electrical activity.

Treatment for respiratory failure depends on:

• Whether it is acute (short-term) or chronic (ongoing)
• How severe it is
• What is causing it

Acute respiratory failure can be a medical emergency. You may need treatment in intensive care unit at a hospital. Chronic respiratory failure can often be treated at home. But if your chronic respiratory failure is severe, you might need treatment in a long-term care center.

One of the main goals of treatment is to get oxygen to your lungs and other organs and remove carbon dioxide from your body. Another goal is to treat the cause of the condition. Treatments may include:

• Oxygen therapy, through a nasal cannula (two small plastic tubes that go in your nostrils) or through a mask that fits over your nose and mouth
• Tracheostomy, a surgically-made hole that goes through the front of your neck and into your windpipe. A breathing tube, also called a tracheostomy, or trach tube, is placed in the hole to help you breathe.
• Ventilator, a breathing machine that blows air into your lungs. It also carries carbon dioxide out of your lungs.
• Other breathing treatments, such as noninvasive positive pressure ventilation (NPPV), which uses mild air pressure to keep your airways open while you sleep. Another treatment is a special bed that rocks back and forth, to help you breathe in and out.
• Fluids, often through an intravenous (IV), to improve blood flow throughout your body. They also provide nutrition.
• Medicines for discomfort
• Treatments for the cause of the respiratory failure. These treatments may include medicines and procedures.

If you have respiratory failure, see your health care provider for ongoing medical care. Your provider may suggest pulmonary rehabilitation.

If your respiratory failure is chronic, make sure that you know when and where to get help for your symptoms. You need emergency care if you have severe symptoms, such as trouble catching your breath or talking. You should call your provider if you notice that your symptoms are worsening or if you have new signs and symptoms.

Living with respiratory failure may cause fear, anxiety, depression, and stress. Talk therapy, medicines, and support groups can help you feel better.

NIH: National Heart, Lung, and Blood Institute

Coronary artery disease (CAD) is the most common type of heart disease. It is the leading cause of death in the United States in both men and women.

CAD happens when the arteries that supply blood to heart muscle become hardened and narrowed. This is due to the buildup of cholesterol and other material, called plaque, on their inner walls. This buildup is called atherosclerosis. As it grows, less blood can flow through the arteries. As a result, the heart muscle can't get the blood or oxygen it needs. This can lead to chest pain (angina) or a heart attack. Most heart attacks happen when a blood clot suddenly cuts off the hearts' blood supply, causing permanent heart damage.

Over time, CAD can also weaken the heart muscle and contribute to heart failure and arrhythmias. Heart failure means the heart can't pump blood well to the rest of the body. Arrhythmias are changes in the normal beating rhythm of the heart.

NIH: National Heart, Lung, and Blood Institute

Heart surgery can correct certain heart problems when other treatments haven't worked or can't be used.

In some cases, heart surgery may be a medical emergency. For example, surgery for a severe heart attack may need to be done right away. In other cases, you can plan heart surgery ahead of time. Some heart surgeries are major operations, such as heart bypass surgery for blocked arteries in the heart. Other surgeries are more minor heart procedures, such as putting in a pacemaker.

There are different types of heart surgery that can help treat many heart conditions:

• An implantable cardioverter defibrillator (ICD) to help prevent sudden cardiac arrest.
• A biventricular pacemaker to coordinate the heart's pumping action so it's more powerful.
• A ventricular assist device to help the heart pump blood.
• A total artificial heart to pump blood for the heart.

The approach a surgeon uses to do heart surgery depends on your heart problem, your general health, and other factors. Approaches to heart surgery include:

• Open-heart surgery (also called traditional heart surgery) is when the surgeon cuts the chest open to reach the heart. Because it's difficult to operate on a beating heart, medicines are used to stop the heart. A heart-lung bypass machine keeps oxygen-rich blood pumping through the body during the surgery.
• Off-pump heart surgery is open-heart surgery on a beating heart without using a heart-lung bypass machine. The surgeon holds the heart steady with a device. Surgeons may use off-pump heart surgery to do coronary artery bypass grafts (CABG), but only in certain cases.
• Minimally invasive heart surgery uses small cuts between the ribs. The cuts may be as small as 2 to 3 inches. The surgeon inserts tools into the chest through the cuts. This type of heart surgery may or may not use a heart-lung bypass machine.
• Robotic-assisted surgery is a type of minimally invasive surgery. The surgeon uses a computer to control tools on the arms of a robot. This allows the surgeon to be very accurate when doing difficult operations.

Like all surgery, heart surgery has risks even though the results are often excellent. The risks include:

• Bleeding
• Infection, fever, and swelling
• A problem from anesthesia (medicine that makes you sleep during surgery)
• Arrhythmia
• Damage to the heart, kidneys, liver, and lungs
• Stroke

The risks of heart surgery tend to be higher if:

• The surgery is an emergency.
• You have other medical conditions, including:
  • Diabetes
  • Kidney diseases
  • Lung diseases
  • Peripheral artery disease (PAD)

NIH: National Heart, Lung, and Blood Institute

Anxiety is a feeling of fear, dread, and uneasiness. It might cause you to sweat, feel restless and tense, and have a rapid heartbeat. It can be a normal reaction to stress. For example, you might feel anxious when faced with a difficult problem at work, before taking a test, or before making an important decision. It can help you to cope. The anxiety may give you a boost of energy or help you focus. But for people with anxiety disorders, the fear is not temporary and can be overwhelming.

Anxiety disorders are conditions in which you have anxiety that does not go away and can get worse over time. The symptoms can interfere with daily activities such as job performance, schoolwork, and relationships.

There are several types of anxiety disorders, including:

• Generalized anxiety disorder (GAD). People with GAD worry about ordinary issues such as health, money, work, and family. But their worries are excessive, and they have them almost every day for at least 6 months.
• Panic disorder. People with panic disorder have panic attacks. These are sudden, repeated periods of intense fear when there is no danger. The attacks come on quickly and can last several minutes or more.
• Phobias. People with phobias have an intense fear of something that poses little or no actual danger. Their fear may be about spiders, flying, going to crowded places, or being in social situations (known as social anxiety).

The cause of anxiety is unknown. Factors such as genetics, brain biology and chemistry, stress, and your environment may play a role.

The risk factors for the different types of anxiety disorders can vary. For example, GAD and phobias are more common in women, but social anxiety affects men and women equally. There are some general risk factors for all types of anxiety disorders, including:

• Certain personality traits, such as being shy or withdrawn when you are in new situations or meeting new people
• Traumatic events in early childhood or adulthood
• Family history of anxiety or other mental disorders
• Some physical health conditions, such as thyroid problems or arrhythmia

The different types of anxiety disorders can have different symptoms. But they all have a combination of:

• Anxious thoughts or beliefs that are hard to control. They make you feel restless and tense and interfere with your daily life. They do not go away and can get worse over time.
• Physical symptoms, such as a pounding or rapid heartbeat, unexplained aches and pains, dizziness, and shortness of breath
• Changes in behavior, such as avoiding everyday activities you used to do

Using caffeine, other substances, and certain medicines can make your symptoms worse.

To diagnose anxiety disorders, your health care provider will ask about your symptoms and medical history. You may also have a physical exam and lab tests to make sure that a different health problem is not the cause of your symptoms.

If you don't have another health problem, you will get a psychological evaluation. Your provider may do it, or you may be referred to a mental health professional to get one.

The main treatments for anxiety disorders are psychotherapy (talk therapy), medicines, or both:

• Psychotherapy can help you recognize and change troubling emotions, thoughts, and behaviors. To be effective, it should focus on your specific anxieties and needs. There are many types; some of the types used for anxiety disorders include:
  • Cognitive behavioral therapy (CBT), which teaches you different ways of thinking and behaving. It can help you change how you react to the things that cause you to feel fear and anxiety. It may include exposure therapy. This therapy focuses on having you confront your fears so that you will be able to do the things that you had been avoiding.
  • Acceptance and commitment therapy may help with some anxiety disorders. It uses strategies such as mindfulness and goal setting to reduce discomfort and anxiety.
• Medicines to treat anxiety disorders include anti-anxiety medicines and certain antidepressants. Some types of medicines may work better for specific types of anxiety disorders. You should work closely with your provider to identify which medicine is best for you. You may need to try more than one medicine before you can find the right one.

Support groups and stress management techniques may also be helpful.

NIH: National Institute of Mental Health

Aplastic anemia is a rare but serious blood disorder. If you have it, your bone marrow doesn't make enough new blood cells. It happens when there is damage to stem cells inside your bone marrow. There are different types of aplastic anemia, including Fanconi anemia.

The causes of aplastic anemia can include:

• Autoimmune disorders, which are the most common cause
• Certain inherited gene changes, such as the one that can cause Fanconi anemia
• Toxic substances, such as pesticides, arsenic, and benzene
• Radiation therapy and chemotherapy for cancer
• Certain medicines
• Viral infections such as hepatitis, Epstein-Barr virus, or HIV
• Pregnancy

In many people, the cause is unknown. This is called idiopathic aplastic anemia.

Aplastic anemia can develop suddenly or slowly. It can be mild or severe. The symptoms of aplastic anemia can include:

• Fatigue
• Weakness
• Dizziness
• Shortness of breath
• Easy bruising or bleeding

Aplastic anemia can cause other problems, including frequent infections and bleeding. It raises your risk of developing a serious blood disorder.

If not treated, aplastic anemia can also lead to heart problems such as an arrhythmia (a problem with the rate or rhythm of your heartbeat), an enlarged heart, or heart failure.

To find out if you have aplastic anemia, your doctor will:

• Take your medical and your family medical histories
• Do a physical exam
• Order tests, such as tests to check if you have low numbers of cells in your bone marrow and blood

If you have aplastic anemia, your doctor will create a treatment plan for you. The plan will be based on how severe the anemia is and what is causing it. Treatments can include:

• Blood transfusions
• Blood and marrow stem cell transplants
• Medicines to suppress your immune system

Because of the risk of blood disorders, your doctor will monitor your condition and screen you for blood disorders regularly.

NIH: National Heart, Lung, and Blood Institute

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.