Caffeine Effects, risks, and cautions

Militha Mihiranga

For many of us, beginning the day with a cup of coffee would be possible. One explanation could be that it gives us a caffeine kick, a modest central nervous system stimulant that instantly increases our alertness and energy. Of course, coffee isn’t the only beverage that contains caffeine. Continue reading to summarise the study on this stimulant’s health effects and information on caffeine’s origins.

Absorption and Metabolism of Caffeine

Trimethylxanthine (1,3,7) is the chemical name for the bitter white powder known as caffeine. Caffeine is absorbed within 45 minutes of consumption, and blood levels peak between 15 and 2 hours later. Coffee, tea, and soda all contain caffeine, which is readily absorbed in the gut and dissolves in water and fat molecules. It can enter the brain. Meals or food-related substances, such as fibres, can slow down the rate at which caffeine levels in the blood peak. A quicker energy boost could result from sipping your morning coffee on an empty stomach instead of after breakfast.

The liver is where caffeine is primarily metabolised. Depending on several variables, its blood retention time can range from 1.5 to 9.5 hours. Caffeine is broken down more quickly by smoking than pregnancy or oral contraception. Caffeine can stay in the body for up to 15 hours while a woman is in her third trimester of pregnancy.

When caffeine is ingested frequently, people frequently build up a “tolerance to caffeine,” which might lessen its stimulant effects unless a higher amount is taken. Withdrawal symptoms, such as irritation, headache, agitation, sad mood, and weariness, frequently follow abruptly discontinuing all caffeine. After a few days of caffeine withdrawal, the symptoms peak, although they usually go away after a week or so. To minimise adverse effects, gradually reducing the dosage may be helpful.

Some standard products with caffeine and the amounts of caffeine are:

  • coffee (250 mL or 1 cup): 40 to 180 mg
  • decaf (250 mL or 1 cup): 2 to 5 mg
  • tea (250 mL or 1 cup): 10 to 110 mg

    Other products that have caffeine include:​

    • stimulants (1 tablet): 100 to 250 mg
    • energy shots or drinks (60 to 360mL​): 4 to 240 mg
    • painkillers (1 tablet): 30 to 100 mg
    • cola drinks (355 mL or 12 oz.): 30 to 60 mg
    • dark chocolate (56 g or two oz.): 40 to 70 mg
    • milk chocolate (56 g or two oz.): 3 to 20 mg
    • Snacks with caffeine (for example, gum, fruit chews, jelly beans): 30 to 50 mg

    Recommended Amounts

    Adults in the U.S. ingest 135 mg of caffeine daily, equivalent to 1.5 cups of coffee (8 ounces = 1 cup). For healthy people, the U.S. Food and Drug Administration deems a daily caffeine intake of 400 milligrams, or around 4 cups of brewed coffee, to be safe. However, the American Society of Obstetricians and Gynecologists advises pregnant women to keep their daily caffeine intake to 200 mg (roughly 2 cups of brewed coffee).

    Children under the age of 12 are advised not to consume any foods or drinks that contain caffeine, according to the American Academy of Pediatrics. Caffeine intake for teenagers 12 and older should be capped at 100 mg daily.

     This is equivalent to two or three 12-ounce cola beverage cans.

    Caffeine and Health

    Many health issues have been linked to caffeine. Caffeine tolerance and responses vary from person to person, partly because of genetic variances. Some people can develop a tolerance to caffeine by frequently consuming it, such as by drinking a cup of coffee each day, which may cause the adverse effects of caffeine to lessen with time. The research below primarily focuses on the health effects of caffeine itself, even though we typically link caffeine with coffee or tea. For more information on the health benefits of coffee, tea, and energy drinks, visit our features on those drinks.

    Effects of caffeine

    There is no safe level of drug use. The use of any drug always carries some risk. It’s essential to be careful when taking any drug.

    Caffeine affects everyone differently, based on the following:

    • 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 following effects may be experienced within 30 minutes after consuming caffeine and may continue for up to 6 hours:

    • feeling more alert and active
    • restlessness, excitability and dizziness
    • anxiety and irritability
    • dehydration and needing to urinate more often
    • higher body temperature
    • faster breathing and heart rate
    • headache and lack of concentration
    • Stomach pains.

    Children and young people who consume energy drinks containing caffeine may also suffer from sleep problems and anxiety.


    If a large amount of caffeine is consumed, it can also cause an overdose.

    Call an ambulance immediately by dialling triple zero (000) if you experience the following effects.

    • tremors
    • nausea and vomiting
    • abdominal pain
    • diarrhoea
    • rapid breathing
    • nervousness/anxiety
    • irritability/agitation
    • very fast and irregular heart rate
    • confusion and panic attack
    • Seizures.

    It is unlikely that a toxic amount of caffeine can be consumed from caffeinated beverages alone. However, large doses of caffeine are dangerous, and there have been deaths from people consuming caffeine in tablet or powder form.

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

    Long-term effects

    Regular, heavy use of caffeine (such as more than 4 cups of coffee a day) may eventually cause:

    • anxiety
    • difficulty sleeping
    • ulcers
    • osteoporosis in post-menopausal women
    • irritability and 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

    Using caffeine with other drugs

    The effects of taking caffeine with other drugs – including over-the-counter or prescribed medications – can be unpredictable and dangerous and could cause:

    The effects of taking caffeine with other drugs – including over-the-counter or prescribed medications – can be unpredictable and dangerous and could cause:

    • Caffeine + alcohol: strain on the body and can mask alcohol’s sedative effects such as falling asleep, leading to drinking more, risk-taking behaviour and increased alcohol-related harms.
    • Caffeine + other psychoactive drugs: caffeine may increase the effects of other psychoactive drugs.2 It also has the potential to interact with over-the-counter and prescribed medications.


    Giving up caffeine after using it for a long time is challenging because the body has to get used to functioning without it. Withdrawal symptoms usually start within 12-24 hours after the last dose. The symptoms can last for around 2-7 days or even longer for people who consume a lot.

    These symptoms can include:

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


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