Caffeine is a widely consumed stimulant substance in many foods, drinks, and supplements. Caffeine can have several health benefits when consumed in moderate amounts but can also cause detrimental effects on health when over-consumed or in individuals with a sensitivity to caffeine.
What is caffeine?
Caffeine is a naturally occurring substance found in or added to many drinks, foods, medications, and supplements. It is a mild stimulant of the central nervous system (CNS) within the methylxanthine class.[1]
Caffeine works by blocking adenosine receptors, which are involved in several functions including alertness, neurotransmitter release, and cardiovascular effects. Caffeine prevents adenosine receptors from releasing signals that cause a feeling of mental fatigue, thus producing its effects on alertness and energy. [2]
Caffeine is the most widely used psychoactive substance, with 80-90% of US adults consuming coffee every day. Most commonly, caffeine is used to reduce fatigue and improve concentration. It is also used in supplements and medications for medicinal purposes, such as to help lung and breathing issues, treat headaches and migraines, and improve athletic performance. [2][3]
Where does caffeine come from?
Caffeine occurs naturally in many plants, including: [2][4][5]
- Cacao beans, leaves, and fruits. Cacao beans are used to make chocolate.
- Coffee beans, leaves, fruits. Coffee beans are used to make coffee.
- Tea leaves, which are used to make various types of tea.
- Kola nuts. Traditionally used for various medicinal purposes and included in cola drinks.
- Guarana plant. The seed of the guarana is processed and added to drinks and energy supplements. It contains four times the amount of caffeine as the coffee bean.
What has caffeine in it?
Caffeine is found in several products, either occurring naturally or as an added ingredient. This includes: [1][4][6]
- Coffee: One cup (8 ounces) contains around 100 mg of caffeine. A cup of instant coffee contains around 60 mg, and a cup of decaffeinated coffee contains 4 mg.
- Tea: One cup of tea contains around 45 mg, while a cup of decaffeinated tea contains around 2 mg. Green tea contains around 30 mg, and most herbal teas contain no caffeine.
- Chocolate: One ounce of dark chocolate contains 24 mg, and one ounce of milk chocolate contains 6 mg.
- Energy drinks: A standard 16-ounce can contain between 80-400 mg of caffeine and a two-ounce shot contains around 200 mg. This varies significantly depending on the energy drink.
- Carbonated drinks: Soft drinks such as cola contain around 40 mg of caffeine per can.
- Supplements: Caffeine supplements tend to contain around 200 mg of caffeine per tablet.
- Medications: Some medications include varying amounts of caffeine, including migraine medication such as Fioricet.
The US Food and Drug Administration recommends that adults consume no more than 400 mg of caffeine daily, which amounts to around four cups of coffee or two energy drinks. Recommendations also include: [1][6]
- No more than 200 mg should be consumed in one serving
- Children under 12 should consume no caffeine
- People between 12-18 years old can consume up to 100 mg
- Pregnant or breastfeeding people can consume up to 200 mg
Side effects of caffeine
Caffeine can cause several effects, some of which may be desired, such as increased energy and alertness, while others may be unpleasant or even dangerous. Side effects of caffeine can range from mild to severe, with the most severe effects occurring with higher or more frequent doses, or in those with caffeine sensitivity.[2]
When consumed, the effects of caffeine emerge within one hour and last around 3-5 hours. It may take longer for these effects to emerge if caffeine is consumed with food. [1][2]
Common side effects of caffeine include: [1][2][6]
- Increased energy
- Restlessness
- Anxiety
- Agitation
- Irritability
- Increased heart rate
- Diarrhea
- Nausea
- Insomnia
- Poor sleep quality
- Increased urination
- Twitching or shaking
- Tolerance
- Dependence
- Withdrawal symptoms
Severe side effects of caffeine may include: [1][2]
- Irregular or rapid heartbeat
- Restricted blood flow
- Seizures
- Hallucinations
- Psychosis
- Disorientation
It is possible to overdose on caffeine. Severe or even fatal effects can occur with the rapid consumption of high doses of around 1200 mg. The risk of consuming dangerously large doses is increased with energy supplements as these often contain very high concentrations of caffeine. [6]
Conversely, research does indicate that there may be several health benefits related to moderate caffeine consumption, including a reduced risk of gallstones, Parkinson's disease, liver cancer, fibrosis, and Type 2 diabetes. [1][7]
Is caffeine addictive?
Caffeine use disorder is listed in the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM-5), indicating that caffeine can be considered an addictive substance. [8]
This diagnosis can include consuming caffeine despite known physical or mental harm, struggling to control or reduce caffeine consumption, and experiencing withdrawal symptoms when reducing or stopping caffeine. [8][9]
Although these criteria can be compared to other addictive substances, caffeine is unlikely to lead to the same level of harm, distress, or impairment as other substance use disorders or addictions. [9]
Caffeine withdrawal
Regular consumption of caffeine can lead to the development of physical dependence. This can occur with small or large quantities of daily caffeine intake and over a short time. Once physical dependence has developed, reducing or stopping caffeine can lead to the onset of stimulant withdrawal symptoms. [3]
Common caffeine withdrawal symptoms include: [1][3]
- Headaches
- Impaired concentration
- Sleep disturbances
- Mood changes such as low mood and anxiety
- Changes in heart rate and blood pressure
- Stomach issues such as constipation, nausea, and stomach pain
Removing caffeine from your diet
People who regularly consume caffeine may notice several effects, such as headaches, nausea, and agitation. If this is the case, it may be a good idea to reduce or stop caffeine consumption. Similarly, those who consume over the recommended daily amount of 400 mg might also benefit from removing caffeine from their diet. [6]
It is recommended not to abruptly stop caffeine consumption, as this can cause the onset of withdrawal symptoms. Gradually reducing caffeine intake can help prevent these symptoms. For example, people who drink four cups of coffee per day might find it helpful to reduce this by one cup every week or two. [3]
It might also be helpful to replace caffeinated beverages with alternatives, such as soda water instead of carbonated soft drinks like cola and herbal teas instead of hot drinks like tea and coffee.
Ensuring regular consumption of vitamins and minerals, such as those found in fruits and vegetables, can help boost energy levels. Drinking a smoothie or eating a piece of fruit can be a good energy booster to replace the first coffee of the day or when lagging in the afternoon.
Similarly, natural techniques to increase energy can be helpful during this time, such as exercise, getting plenty of sleep, and staying hydrated. [10]
Removing caffeine from your diet can provide several health benefits, including improved sleep, concentration, mood, and digestive health, and reduced headaches and anxiety. [11]
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