Key Takeaways
  • Caffeine’s effects can last anywhere between 2 and 12 hours after intake.
  • Individual sensitivity to caffeine varies and impacts the time it takes to wear off.
  • Avoid consuming caffeine at least eight hours before bedtime.

While stimulant effects usually begin within an hour after caffeine consumption, it can take several hours for those effects to wear off. It takes even longer for caffeine to be cleared from the body. 

Exactly how long it takes caffeine to wear off varies from person to person. The time required for just half of the total caffeine to be eliminated from the body—known as the half-life—is anywhere from 2 to 12 hours

Around 90% of adults eat or drink products containing caffeine every day, mainly because it can help with waking up in the morning and feeling alert throughout the day. However, these same effects can become challenges at bedtime. 

Because caffeine can persist in a person’s system, consuming it too late in the day can make it more difficult to sleep well at night. For this reason, many experts recommend avoiding caffeine within eight hours of sleep. 

Learning about how caffeine affects the body, how much caffeine is safe to consume, and how late is too late to drink caffeine can serve as a first step to making sure that caffeine consumption does not interfere with sleep.

How Caffeine Affects the Body

After ingestion, caffeine is quickly absorbed through the gastrointestinal system . Caffeine has very high bioavailability, which means that nearly all of the caffeine consumed is taken up by the body.

Caffeine generally reaches peak levels within an hour after consumption. Then, the liver and kidneys process and eliminate caffeine through the urine. 

Although there can be individual variation, caffeine usually affects the body in a number of ways:

  • Stimulating the central nervous system as well as parts of the brain associated with breathing and blood flow 
  • Triggering the release of certain hormones and neurotransmitters 
  • Elevating blood sugar
  • Increasing the production of urine and stomach acid 
  • Accelerating digestion 
  • Increasing blood pressure

As a result of these effects, caffeine can make a person feel more awake, alert, and energized. It can also help a person feel more social and temporarily improve their athletic performance. Caffeine even counteracts the effects of sleep loss, improving thinking, memory, and attention in people with jet lag and shift work disorder.

The effects of caffeine on alertness and sleep are thought to be related to its impact of adenosine . Adenosine is a chemical naturally produced in the body. It accumulates while a person is awake, which steadily increases the pressure to sleep. Caffeine blocks adenosine’s effects in the brain, explaining caffeine’s ability to reduce feelings of tiredness.

Relatedly, caffeine can disrupt the body’s natural sleep-wake cycle, making it harder to fall and stay asleep, lowering sleep quality, and reducing deep sleep. Some research suggests that occasional caffeine users may be more sensitive to the disruptive effects of caffeine on sleep.

For regular users, the body can get used to caffeine intake, and they may need to increase caffeine consumption over time to get the same stimulant effects. This also means that withdrawal can occur if caffeine consumption is abruptly stopped.

How Long Does Caffeine Last?

It takes from 15 to 60 minutes to feel the effects of caffeine. The effects may continue for around three to five hours, though it takes much longer for all the caffeine to leave the body. 

How long caffeine lasts depends on how quickly it is absorbed and processed by the body. The absorption, metabolism, and half-life of caffeine can vary substantially between different people and at different times based on a variety of factors. Examples of these factors include: 

  • Genetics 
  • Sex 
  • Age 
  • Body weight
  • Being pregnant
  • Having certain medical conditions 
  • Taking oral contraceptives 
  • Drinking alcohol or smoking cigarettes 
  • Being at a high altitude
  • Eating before consuming caffeine 

Because so many factors can impact the rate at which caffeine affects and is cleared from the body, it is difficult to say exactly how long caffeine lasts in a person’s system. In most cases, half of the caffeine is cleared in 4 to 6 hours , but in any specific situation the half-life can range from 2 to 12 hours. 

A consequence of caffeine’s ability to stay in the body over an extended period is that it has the potential to disrupt sleep. This is most likely to occur when caffeine is consumed late in the day, but some research suggests that it is possible for caffeine to have a lingering effect on sleep for up to 16 hours after consumption.

How Much Caffeine Is Safe to Drink?

Most adults can safely consume up to 400 milligrams of caffeine each day, which is roughly equivalent to four cups of coffee

The American Academy of Pediatrics discourages the use of caffeine in children and adolescents because they may be more vulnerable to sleep loss and other potentially harmful effects of caffeine. Despite these recommendations, national surveys have found that more than 75% of children over the age of 5 consume caffeine.

People who are pregnant or breastfeeding should talk to their doctor about the safety of caffeine use. Although caffeine can cross the placenta to reach the fetus, its effects on fetal health are unknown. There is no evidence that consuming less than 200 milligrams of caffeine per day increases the risk of miscarriage, premature birth, or birth defects.

Other individuals should be cautious about their use of caffeine and talk to their doctor about safe levels of consumption. This includes people with:

  • Sleep disorders
  • Migraines or regular headaches
  • Anxiety 
  • Acid reflux or stomach ulcers 
  • Cardiovascular disease or heart arrhythmia 
  • Liver or kidney disease 
  • Seizures

Caution with caffeine intake is also recommended for people taking medications like stimulants and some antibiotics, asthma drugs, and heart medications. 

Caffeine poisoning, also called caffeine toxicity, is an uncommon but dangerous condition that occurs if a person consumes too much caffeine. Symptoms of caffeine poisoning may begin after consuming around 1,200 milligrams. 

Caffeine poisoning is rarely related to consuming coffee or tea. Instead, it is usually linked to products with a higher concentration of caffeine. Most emergency room visits related to caffeine poisoning are from young adults who mixed energy drinks with alcohol or other substances.

What Contains Caffeine?

Caffeine is naturally present in at least 60 plants, including coffee beans, tea leaves, cacao pods used to make chocolate, kola nuts used in soft drinks, and guarana berries used in energy drinks.

Caffeine is also produced synthetically and is added to various foods, drinks, medications, and other products. Caffeine is included in some pain medications, cold remedies, and diet pills.

Most caffeine consumed in the United States comes from drinks like coffee, tea, soft drinks, and energy drinks. Coffee is the main source of caffeine for adults in the U.S., where the average person drinks around two cups per day.

The amount of caffeine contained in coffee depends on the source of the coffee beans and how the coffee is processed and brewed. Even decaffeinated coffee contains a small amount of caffeine.

CoffeeServing SizeApproximate Caffeine Content
Brewed Coffee8 ounces70-140 milligrams
Decaf Coffee8 ounces3-12 milligrams
Espresso1 ounce40 milligrams

In tea, the amount of caffeine depends on the type of tea, how long it was steeped, and the serving size. Many teas are produced from the Camellia sinensis plant and naturally contain caffeine. The exception is herbal teas, which are made from other plants and typically do not contain caffeine.

TeaServing SizeApproximate Caffeine Content
Black, green, or white tea8 ounces40-120 milligrams
Bottled Teas12-16 ounces10-100 milligrams

Soft drinks and energy drinks are a common source of caffeine in the U.S., particularly for children and adolescents. While the FDA limits the amount of caffeine contained in certain soft drinks, many energy drinks are sold as dietary supplements and are not required to stay within this limit. Because some energy drinks can contain very high amounts of caffeine, they can be dangerous when mixed with alcohol or other substances.

DrinksServing SizeApproximate Caffeine Content
Regular or diet soda12 ounces0-70 milligrams
Energy drinks8-16 ounces50-300 milligrams
Hot cocoa8 ounces3-13 milligrams

Finally, caffeine is contained in chocolate and added to a variety of foods such as ice creams, snacks, candies, and gum.

FoodServing SizeApproximate Caffeine Content
Coffee-flavored ice cream8 ounces 50-85 milligrams
Dark chocolate (55%)100 grams125 milligrams
Milk chocolate (33%)100 grams45 milligrams

How Late Should You Drink Caffeine?

Experts typically recommend avoiding caffeine at least eight hours before bedtime. While an afternoon coffee, tea, or energy drink may increase alertness and combat drowsiness, consuming caffeine too late in the day can lead to trouble falling and staying asleep at bedtime. 

For people who are more sensitive to the effects of caffeine, eight hours before bedtime may not be enough. For them, it may be necessary to stop caffeine consumption even earlier in the day.

Anyone who has sleeping problems or significant daytime sleepiness should talk with their doctor and review their sleep-related habits. A doctor can provide specific guidance about improving sleep, including any potential changes to daily caffeine consumption as part of their everyday diet.

Learn more about our Editorial Team

11 Sources

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