Caffeine: How Much Is in Your Drink, What It Does, and Who Should Cut Back

What it is

Caffeine is a bitter substance found naturally in more than 60 plants, including:

• coffee beans;
• tea leaves;
• kola nuts, which flavor colas;
• cacao pods, used for chocolate.

Synthetic caffeine is added to some pain relievers, cold medicines and over-the-counter alertness pills, and to energy drinks and "energy-boosting" gums and snacks.

How much is in a drink

Amounts vary a lot, but generally:

What it does

• Stimulates the central nervous system — you feel more awake and energetic.
• Acts as a diuretic, ridding the body of extra salt and water through urine.
• Raises stomach acid, sometimes causing an upset stomach or heartburn.
• May interfere with calcium absorption.
• Raises blood pressure.

It peaks in the blood within one hour, and you may feel it for four to six hours.

Too much

For most people, up to 400mg a day isn't harmful. Too much can cause:

• restlessness and shakiness;
• insomnia;
• headaches and dizziness;
• a fast heart rate;
• dehydration;
• anxiety;
• dependency, needing more for the same effect.

Some people are more sensitive than others.

Energy drinks

They have added caffeine, sometimes more than the label says, plus sugars, vitamins, herbs and supplements. Makers claim they boost alertness and physical and mental performance, which has made them popular with American teens and young adults.

• Evidence: limited data suggest they may briefly improve alertness and endurance; there's not enough to show they build strength or power.
• Risks: large amounts of caffeine make them dangerous, and their sugar can add weight and worsen diabetes.
• With alcohol: dangerous. Caffeine can mask how drunk you are, leading you to drink more and make bad decisions.

Who should limit or avoid it

Ask your health care provider if you:

• are pregnant — caffeine crosses the placenta to your baby;
• are breastfeeding — a little passes to your baby;
• have sleep disorders, including insomnia;
• have migraines or other chronic headaches;
• have anxiety;
• have GERD or ulcers;
• have an arrhythmia, a problem with the rate or rhythm of your heartbeat;
• have high blood pressure;
• take certain medicines or supplements — stimulants, some antibiotics, asthma and heart medicines. Ask about interactions with anything you take.

Children and teens shouldn't have as much as adults; children can be especially sensitive.

Withdrawal

Stop suddenly after regular use, and you may get headaches, drowsiness, irritability, nausea and trouble concentrating. These usually pass in a couple of days.

Sources

Based on "Caffeine," MedlinePlus, National Library of Medicine; a work of the United States government in the public domain.