Caffeine is a drug (or chemical) found in plants. It can be harmful for both humans and animals if a large amount is consumed. If a person ate 10-13 grams of caffeine quickly, between 80-100 cups of coffee, it would kill them.

Source 
Caffeine is the main drug that is in coffee. Coffee comes from a tree. The seeds of the tree are roasted to make coffee.

Caffeine comes from other plants as well. It is in guarana, yerba maté, cacao, and some plants used to make tea. The plants use caffeine as a pesticide. This is a chemical that kills insects if they eat the plant. It is the way the plant protects itself.

Caffeine was first extracted from cocoa beans into its purest form which is a white powder and the word originated from the German word “kaffee” and the French word “café” which both mean caffeine.

It is called guaranine when it comes from the guarana plant and theine when it comes from a tea plant. It is called mateine in the mate drink. This drink is an infusion made with Yerba mate.

What caffeine is 

Caffeine is a stimulant drug. A stimulant is a drug that increases body actions like heart rate, blood pressure, and metabolism. It makes a person more awake and alert.

Caffeine also is a diuretic. This means it makes a person make more urine (the waste liquid a person makes).

The caffeine chemical is called a xanthine alkaloid. This is a group of chemicals that are stimulants. Some xanthine alkaloids (like theophylline) are used to help asthma.

What caffeine is used for 
The biggest use of caffeine is as a stimulant. People drink coffee and other drinks with caffeine to stay awake.

Doctors sometimes use caffeine as a medicine. It is used for headaches (head pain). It is sometimes used to help premature (born very early) babies to breathe. The short-term risk of this treatment seems to be that the babies treated gain less weight than usual.

Caffeine is sometimes given to people after a lumbar puncture. This is a test to see if someone has meningitis.

In the beginning caffeine was found to relieve hunger, so it was used for weight loss. That did not last because people were using too much. Caffeine can be a very dangerous drug when not used in the right way.

Caffeine also has medicinal properties. It is used in many over the counter medicines, such as Excedrin, Midol and Anacin. When combined with other analgesics, caffeine can help to alleviate headaches and cramps.

Problems with caffeine 

The largest problem with caffeine is addiction. This is when people get bad symptoms when they do not have the drug. When people have withdrawal (feel bad because they do not have the drug) they drink more. This makes them feel better. But if they cannot get more, they are likely to feel some of the symptoms listed below:
 Headaches
 Being tired or need to sleep
 Caffeine inhibits sleep and in the long-term alters brain functions
 Sleep deprivation leads to a weakened connectivity between the amygdala and medial prefrontal cortex which regulate mood and emotion.
 This causes the consumer to feel irritable, tired, restlessness, and anxious.
 Nausea (feeling like vomiting)

Caffeine can also hurt people if they drink a lot at once. If someone takes too much of a drug at once it is called an overdose. Caffeine overdose is a medical diagnosis. It is called: Caffeine-Induced Organic Mental Disorder or Caffeine Intoxication. People with this can have these symptoms:
 Very bad feelings like:
 Paranoia (feeling as if people are about to hurt the person)
 Restlessness or nervousness (with the person feeling like he cannot sit down or rest)
 Anxiety (very bad worry)
 Muscle movements that cannot be stopped
 Very fast heart rate
 Abnormal heart rhythms (even heart stopping)
 Very high blood pressure
 Vomiting
 Confusion (not knowing who the person is or where he/she is)

Caffeine helps for 
Caffeine also has some strong advantages:
 Lower risk of coronary disease
 Cut stroke risk
 Speed up metabolism
 Increases memory
 Helps ward off Alzheimer’s
 Reduces kidney stone risk

How much caffeine is safe 
250–300 mg of caffeine a day is a moderate amount. That is as much caffeine that is in three cups of coffee (8oz each cup). More than 750–1000 mg a day is a significant amount, but is very unlikely to kill someone. The Lethal Dose 50 of caffeine is 192 mg per kilogram, in rats. In humans, it is between 150 and 200 mg per kilogram (70-90 per pound.)

Caffeine is in many drinks and foods. This is approximate amounts of caffeine in some food and drink:

 Brewed coffee - 40 to 220 mg in a cup
 Instant coffee - 30 to 120 mg in a cup
 Decaffeinated coffee (with most caffeine taken out) - 3 to 5 mg in a cup
 Tea - 20 to 110 mg in a cup
 Soda drinks with caffeine - 36 to 90 mg in 12 ounces. Some people think that soft drinks which are light in color do not contain caffeine. This is not always true.
 Milk chocolate - 3 to 6 mg in an ounce
 Bittersweet chocolate - 25 mg in an ounce

One ounce – abbreviated oz - is 30ml.

A 'cup' is 8 oz (240ml.)

Different ways to get 200mg of caffeine

References

Other websites

Scientific information 
 eMedicine Caffeine-Related Psychiatric Disorders
 The Consumers Union Report on Licit and Illicit Drugs, Caffeine-Part 1 Part 2
 The Physician and Sportsmedicine: Caffeine: A User's Guide 
 Caffeine: Psychological Effects, Use & Abuse 
 Caffeine Withdrawal Recognized as a Disorder
 Is Caffeine a Health Hazard?

Others 
 Caffeine Withdrawal Symptoms
 Caffeine: How Stuff Works
 Caffeine: The most popular psychoactive drug, Broke but Shredded, January 2022
 Erowid Caffeine Vaults
 #caffeine! - The Caffeine Information Archive
 Naked Scientists Online: Why do plants make caffeine?
 Alcohol and Drugs History Society: Caffeine news page
 Coffee: A Little Really Does Go a Long Way, NPR, September 28, 2006
 Does coffee really give you a buzz? by John Triggs in the Daily Express April 17 2007
 Burgower, Rachael. “The Effects of Energy Drinks on Sleep and Daily Functioning.” ProQuest   LLC, 2014, pp. 1–59. ProQuest, https://search.proquest.com/docview/1642026146.

News 
 National Post: Caffeine linked to psychiatric disorders

Organic compounds
Drugs
Former good articles