Caffeine

How is caffeine used?

Caffeine is used in a number of different products. The amount of caffeine in products can vary dramatically, so it’s always best to check the label. The average amounts are listed below.

Average amounts⁶

Effects of caffeine

The use of any drug can have risks. It’s important to be careful when taking any type of drug.

Caffeine can affect everyone differently, based on:

• size, weight and health
• whether the person is used to taking it
• whether other drugs are taken around the same time
• the amount taken
• the environment (where the drug is taken).

Onset and duration of effects

When drunk or consumed as food, the effects of caffeine are usually experienced within 5 – 10 minutes, and can last for up to 6 hours.⁷

Caffeine levels in the blood usually peak about an hour after use. But, taking caffeine with food can slow how quickly it’s absorbed into the body.^{3, 8}

The body can usually break down small to moderate amounts of caffeine quickly. Larger amounts can take longer to leave the body.³

Effects

Effects can include:

• feeling more alert and active
• restlessness
• excitability
• dizziness
• Anxiety
• irritability
• diarrhoea
• dehydration
• needing to urinate more often
• higher body temperature
• faster breathing and heart rate
• increased blood pressure
• headache
• lack of concentration
• stomach pains.^{3, 4}

People who consume energy drinks containing caffeine may also suffer from sleep problems and anxiety.^9-12

Overdose

It is unlikely that a toxic amount of caffeine can be consumed from caffeinated beverages alone.¹³

However, large doses of caffeine are dangerous and there have been deaths from people consuming caffeine in tablet or powder form.¹⁴

Your risk of overdose can also increase if you mix caffeine with alcohol or other drugs, including medications.

Call triple zero (000) and request an ambulance if you or someone else has any of the following symptoms (emergency services are there to help and can provide more instructions).

Signs of caffeine overdose can include:

• nausea and vomiting
• abdominal pain
• unconscious or non-responsive
• tremors, spasms, or seizures
• feeling tired or fatigued
• heart attack symptoms such as:
• difficulty breathing
• sharp pain/discomfort in chest, arm, shoulder, back, neck, or jaw
• severe agitation, confusion, or panic
• racing heartbeat
• hot, flushed (red), or sweaty skin.^{15, 16}

People who use caffeinated products, such as weight loss products or powdered caffeine for performance and image enhancing aids, should ensure they are aware of the recommended reasonable amount of caffeine to consume per serving. 

Learn more on overdose and drug-related emergencies.

Mixing with other drugs

Mixing caffeine with other drugs can have unpredictable effects and increase the risk of harm.

• Caffeine and alcohol: can cause strain on the body and mask alcohol’s sedative effects such as falling asleep, leading to drinking more, risk taking behaviour, and increased alcohol related harms.
• Caffeine and stimulants (such as amphetamines, cocaine, methamphetamine (ice)): can increase strain on heart, especially for people with pre-existing heart conditions. Some people find the combination uncomfortable.^{2, 7, 17, 18}

Using more than one drug or type of drug at the same time is called polydrug use.¹⁵

Reducing harm

There are ways you can reduce the risk of harm when using caffeine.

• Healthy adults should drink no more than 4 cups of coffee per day.
• Children and young adults should avoid excessive consumption of energy drinks and coffee. 
• Pregnant of breastfeeding women should limit their coffee intake to no more than 200 mg per day.
• Avoid mixing caffeine and alcohol as the caffeine can mask the effects of the alcohol which can lead to drinking more, taking risks and increased alcohol related harms.

Coming down

Caffeine blocks the receptors in the brain responsible for feeling tired. This causes a build-up of adenosine (the main sleep chemical). Once the caffeine has worn off, the extra adenosine starts affecting those receptors.^{3, 19}

This can cause you to feel tired or sluggish, and is sometimes called a caffeine comedown or an afternoon ‘caffeine crash’.⁷

Other caffeine comedown effects include:

• difficulty concentrating or focusing
• brain-fog
• anxiety
• low mood or depression
• irritability
• wakefulness.⁷

Some ways to reduce your risk of experiencing a caffeine crash are:

• waiting at least 1 hour after waking up to have your morning coffee or caffeine drink, as having caffeine first thing in the morning can affect your natural sleep-wake cycle and make the effects of a caffeine crash worse.
• making sure that there is food in your stomach when having caffeine.
• leaving time between cups of coffee or caffeine drinks.¹⁹

Long-term effects

Long-term effects can vary depending on how much, how often and how caffeine is consumed.

Regular use of caffeine (such as more than 4 cups of coffee a day) may eventually contribute to:

• anxiety
• difficulty sleeping
• ulcers
• osteoporosis in post-menopausal women
• irritability
• headaches
• dizziness and ringing in the ears
• muscle tremor
• weakness and fatigue
• rapid heart rate and quickened breathing rate
• poor appetite, nausea, vomiting and diarrhoea
• increased thirst, frequent urination or increased urine volume
• irregular heart rate or rhythm
• low blood pressure with faintness or falls
• seizures, confusion or delirium.^{2, 4}

Caffeine and mental health

Caffeine can affect mental health differently depending on the person, how much caffeine they usually have, and their individual risk factors.^{8, 19}

Lower amounts of caffeine (1 - 2 cups of coffee) may improve mood and alertness, while higher amounts (more than 2 cups) can increase feelings of anxiety, stress, and restlessness.^{8, 19, 20}

One of caffeine’s main effects is making you feel less tired. This can affect how long you sleep, and how well you sleep.²⁰

Getting enough good-quality sleep is important for your mental health. The ideal amount of sleep is 6 – 8 hours per night.²¹

Having too much caffeine during the day or having it close to bedtime (within 6 hours of bed), can affect your sleep. This can contribute to mental health concerns such as anxiety, stress, and depression.^{20, 22}

Recent evidence has also linked energy drinks containing caffeine to an increased risk of anxiety and depression. This may be because of the higher than normal amounts of caffeine in these drinks, or due to the negative impact that caffeine can have on sleep.¹²

People experiencing anxiety, heart conditions, or sleep problems may be more sensitive to caffeine, which can make their symptoms worse.³

Tolerance

Regularly using caffeine can lead to developing a tolerance, which means you need to take larger amounts to get the same effects.^{7, 19}

Dependence

People who regularly use caffeine may become dependent. They may feel they need to use caffeine to go about usual activities like working, studying and socialising, or just to get through the day.7

Withdrawal

Withdrawal refers to the symptoms that can occur when someone who is dependent on a drug, or who has been using it regularly over time, stops or reduces their use.²³

Withdrawal can include physical symptoms (such as headaches, or nausea) and psychological symptoms (such as anxiety, or depressed mood).²³

Symptoms - including how strong they are and how long they last - will vary depending on the type of drug and a person’s history of use.²³

Withdrawal symptoms

Reducing, or stopping using caffeine after a period of regular use can lead to withdrawal symptoms, including:

• headache
• extreme fatigue or drowsiness
• nausea
• anxiety/irritability
• sweating
• depressed mood or irritability
• difficulty concentrating
• flu-like symptoms (nausea, vomiting or muscle pain/stiffness).²

Withdrawal symptoms usually start within 12-24 hours after the last dose. The symptoms can last for around 2-7 days, or longer for people who consume a lot.²

Pregnancy and breastfeeding

Before pregnancy

There’s limited information about the impacts of caffeine on fertility. Some research suggests that it can take longer for people who consume a lot of caffeine to get pregnant, and they may have higher rates of miscarriage.²⁴

During pregnancy

Caffeine crosses the placenta from the pregnant person to the baby and will have a similar dose in the baby’s system. And during pregnancy caffeine is cleared from the body more slowly, which can lead to higher levels of caffeine in you and your baby.^{3, 25}

Caffeine may also make you feel more sick than usual during pregnancy, and can impact your sleep, possibly making you more prone to insomnia.²⁵

If you’re pregnant, it’s recommended to have no more than 200mg of caffeine a day. This is the equivalent of about one cup of coffee, depending on the beans, the way the coffee is made and strength of the brew.²⁵

High doses of caffeine can be dangerous for your unborn baby, increasing the risk of miscarriage, stillbirth, and low birth weight. The risk of low birth weight appears to increase with higher doses of caffeine.^{3, 25}

Some evidence has linked caffeine exposure during pregnancy to a higher risk of obesity and other metabolic health problems in children.^{3, 25}

After pregnancy

Caffeine can be passed to the baby through breastmilk. If you choose to breastfeed, it’s recommended to have no more than 200mg of caffeine a day.3, 25

Waiting a while after you have had coffee, or waiting until after breastfeeding to have a coffee, gives your body a chance to process the caffeine before you next feed.

Getting help

If your use of caffeine is affecting your health, family, relationships, work, school, financial or other life situations, or you’re concerned about someone, there is help and support. 

• Call the National Alcohol and Other Drug Hotline on 1800 250 015 for free and confidential advice, information and counselling about alcohol and other drugs.
• Search our Help and Support directory to find your preferred support, by adding your location or postcode and filtering by service type