Caffeine acts quickly, and many people notice the effects within minutes. They last until the body fully metabolizes the drug. This duration depends on several factors.
Each person will feel the effects differently, and some may last longer than others. People who are pregnant or have difficulty sleeping should be careful about timing their caffeine intake and may want to avoid it altogether.
How long does it take to metabolize caffeine?
Caffeine may have a greater effect on people who are sensitive to it.
Caffeine has a half-life of about 5 hours.
Someone who consumes 40 milligrams (mg) of caffeine will have 20 mg remaining in their system after 5 hours.
When do effects peak?
Levels of caffeine peak in the blood within about 15–45 minutes of consumption.
They are then quickly metabolized by the liver.
Most people notice the strongest effects during this time, and many report feeling jittery, needing to urinate, and having sudden bursts of energy. These symptoms tend to go away as the caffeine starts to break down.
Can a person build up a tolerance?
As the body becomes resistant to the drug, people who regularly consume caffeine may barely notice its effects.
However, for someone who is very sensitive to caffeine, effects may persist for hours or until the next day.
How long do effects last?
There is no set time limit. The duration of the drug's effects depend upon the dosage and on personal factors, including age, body weight, and how sensitive a person is to caffeine.
Foods and drinks that contain caffeine
Caffeine is usually found in beverages, including:
- coffee and drinks such as espressos, lattes, and cappuccinos
- black, green, and white tea
- yerba maté
- many soft drinks
- energy drinks
Even decaffeinated coffee contains some caffeine, and people who are very sensitive to caffeine should avoid it.
Caffeine can also be found in foods, such as:
- chocolate and products containing it, such as hot cocoa
- coffee or mocha ice creams
- guarana seeds and beverages
- some protein and energy bars
- pre-workout drinks and powders
Caffeine is also a common ingredient in weight loss pills and over-the-counter headache medicines, including Excedrin.
How much caffeine is in each product?
Energy drinks have higher levels of caffeine than tea or coffee.
The amount of caffeine in products like coffee and tea varies, but the American Academy of Sleep Medicine has listed the following estimates:
- 8 ounces (oz) of brewed coffee – 95 mg
- 1 oz of espresso – 64 mg
- 8 oz of brewed tea – 47 mg
- 16-oz average energy drink – 158 mg
- 12-oz average caffeinated soda – 45 mg
- 1.55-oz milk chocolate candy bar – 9 mg
Drugs that contain caffeine will display exact amounts on their labels.
Caffeine and breast-feeding
People are usually warned not to consume caffeine while pregnant, as it can pose risks to the mother and child. While these risks diminish after birth, caffeine can affect a baby who is breast-fed.
Small amounts of caffeine can be transferred through breast milk, so anyone who is nursing should limit their caffeine intake before feedings. Most babies older than 3 months can tolerate these relatively small amounts. One study found that regular caffeine consumption by nursing women had little or no consequences on sleep patterns of babies and children aged over 3 months.
However, large amounts of caffeine can make babies fussy and irritable. It can also lead to trouble developing regular sleep patterns and other negative effects.
A doctor can provide specific recommendations, but there should generally be a 1–2-hour gap between caffeine consumption and nursing.
How does caffeine affect sleep?
The overall effects of caffeine can last throughout the day. The drug can linger in the body and may have subtle consequences, even after the noticeable effects have worn off.
Caffeine can lead to sleep of a lesser quality and even disrupt sleep patterns, depending on a person's sensitivity and how much they have consumed.
Most adults can safely consume 200–300 mg per day, and exceeding this amount can lead to sleep issues.
What to do when too much caffeine disrupts sleep?
If someone suspects that their caffeine intake is causing sleepless nights, they should lower their consumption until they determine the right limit.
It may also help to practice relaxation techniques before bed, such as gentle yoga or breathing exercises.
Caffeine can be a helpful stimulant, but excessive consumption can mask underlying sleep disorders. People who need coffee or tea to wake up every morning may be unwittingly compensating for sleep issues.
Develop a regular sleep schedule by going to bed and waking up at around the same times each day. This can help the body to regulate itself, and reduce the need for stimulants like caffeine.
Side effects of caffeine
Caffeine may cause diarrhea or an upset stomach.
People will quickly realize when they have had too much caffeine. Be aware of the following symptoms:
- a stomachache
- a rapid or irregular heartbeat
- an increased rate of breathing
- feeling fidgety or restless
- anxiety attacks
People with kidney or liver problems may find their health gets worse when they have caffeine.
In some cases, caffeine can make fatigue worse. If someone is exhausted, they may benefit more from napping or practicing a relaxation technique before resuming activity.
Like other drugs, it is possible to become dependent on caffeine, and going without it can lead to symptoms of withdrawal.
Symptoms of caffeine withdrawal
People who stop consuming caffeine often complain of withdrawal. Symptoms include:
- general fatigue
- crankiness or irritability
- muscle pain
- nausea or an upset stomach
- a lack of focus
- headaches or migraines
These symptoms may resolve when a person consumes caffeine again. If a person is determined to stop, withdrawal symptoms often pass within a few days.
When a person who regularly consumed high amounts of caffeine stops suddenly, they may experience more severe withdrawal symptoms.
Rather than quitting abruptly, it may be better to gradually reduce caffeine intake until it can be eliminated without symptoms.
The effects of caffeine typically last for a few hours, unless someone has consumed a high amount or is especially sensitive to the drug.
Caffeine lingers in the body and may disrupt sleep patterns, even after noticeable effects have worn off.
While it is generally considered safe to consume caffeine while breast-feeding, it may be a good idea to cut off consumption 1–2 hours before a feed.
Anyone who regularly has trouble sleeping or waking up should discuss underlying sleep disorders with a doctor.
It may be a good idea to explore natural ways to increase energy levels.