White porcelain cup of freshly brewed coffee close-up arranged with two sandwich-biscuits spoon and plate on dark background

Is Caffeine Bad For You?

Coffee cookies - Is Caffeine Bad For You?


They say caffeine is the most widely consumed psychotropic drug in the world.


Billions of people rely on caffeine from various sources each day to get their mornings off and running. Some 80% of the world’s population consumes a caffeinated product every day (1).   Myself included.


Mention coffee or tea and everyone thinks of caffeine; more often than not, in a negative way. But is it really all bad?


I will tackle this and other questions about caffeine, its impact on health, answer the question about how much is too much and more. So grab a cup of coffee or tea, sit back and learn about the wonderful world of all things caffeine!

What is caffeine?

Oh caffeine, where did thou come from? There’s evidence that tea was being brewed as a beverage as far back as 2727 BC (1). Regarding coffee’s story, the one I’ve heard told over and over again is that an Ethiopian shepherd noticed his goats would get bursts of energy after nibbling, on what is now known as coffee, the coffee ‘cherry’ specifically (1).


I remember using tea leaves in my high school chemistry class as a source of caffeine. Through various steps, we isolated the pure white powder. The stuff that’s naturally found in various plants and added to energy drinks, soft drinks, and medications.


Caffeine in Foods. A Comprehensive Review on Consumption, Functionality, Safety, and Regulatory Matters


Caffeine is a naturally occurring compound (alkaloid, specifically 1, 3, 7-trimethylxanthine) found in over 60 plants including coffee, tea leaves, cocoa beans, guarana berries, kola nut, and yerba mate. In plants that contain caffeine, caffeine acts as a natural pesticide. Insects best stay away and not nibble, or it’s lights out for them. Caffeine also prevents seeds from other nearby plants from germinating. This survival feature favours caffeine-containing plants by ensuring there’s less competition for resources.


There’s no chemical difference between naturally sourced and synthetic caffeine. They’re identical and have the same biological effects once consumed.


Caffeine - Is Caffeine Bad For You?

How does caffeine work?

Caffeine’s reputation is well known; it helps you feel more alert.


Caffeine is a central nervous system (CNS) stimulant. It acts primarily on the brain and spinal cord. By doing so, it helps to prevent tiredness and fatigue. It does so by blocking the effects of adenosine which generally has an inhibitory effect on nerve cells; it calms them (2).  Adenosine levels normally build up throughout the day which helps to relax your brain and nerves, preparing you for sleep later on.


Adenosine has to bind to receptors on your brain and the nerves in your spinal cord for it to do its job. Because caffeine has a similar chemical structure as adenosine, caffeine will bind to the receptor instead. The difference is, caffeine doesn’t inhibit the activity of your CNS the way adenosine does, ergo, you won’t feel tired (3).


Caffeine also stimulates the release of the neurotransmitters dopamine and noradrenaline (3). Dopamine is the neurotransmitter tied to reward and pleasure; one of the reasons why you get that ‘aahh’ feeling after the first couple of sips. Both dopamine and noradrenaline have antidepressant properties which explain why coffee consumption is associated with less depression (4).


It will have another effect, especially if you consume too much caffeine. Caffeine increases the release of the hormone adrenaline from your adrenal glands. Adrenaline is responsible for that jittery feeling you get when really stressed out, or after perhaps after a serious altercation with someone. If you’ve ever had an accident or near accident, adrenaline is responsible for that post-event shaking.


Anyone who’s gotten more of a buzz or lift from coffee after about 3 small servings, is getting their ‘energy’ from adrenaline, not caffeine. Of course, caffeine sensitivity will vary from person to person. Be mindful of your tolerance and any caffeine side effects of concern.


PRO TIP: go easy on the caffeine as too much can cause too much adrenaline release. This will lead to ‘jitters’, the sensation of increased anxiety, agitation, and over-stimulation of your CNS.


Sources of caffeine

Everyone knows about the caffeine in coffee and the caffeine in tea but there several other possible sources. These include any of the plants mentioned above in the introduction, as well as, caffeinated sports drinks, juices, and waters. Then there’s the caffeine in Red Bull and other energy drinks.


Parents often ask about and are rightfully concerned about, the caffeine in Coke and other soft drinks not to mention so-called ‘energy shots’ like 5 Hour Energy. Coffee and tea are the main sources of caffeine for adults. Soft drinks, and energy drinks, are the main sources for children and youth.


Another common, often forgotten about the source of caffeine is medications.  In those medications that contain caffeine, caffeine’s impact has been considered and deemed safe. But not all medications are safe to be mixed with caffeine and caffeine can interact with them. Whenever medications are being considered, be sure to ask about possible interactions (4).

Energy Drinks - Is Caffeine Bad For You?

How does caffeine impact your body?

This is a common question I get from clients and patients. They want to know how caffeine affects them.

Central nervous system

As stated above, caffeine binds to adenosine receptors and is considered an adenosine antagonist. By blocking the action of adenosine, neurons don’t get the signal to ‘calm’ their activity. Caffeine increases energy metabolism in the brain; more energy, better functioning. The ‘alerting’ effects of caffeine are also related to its action on serotonin neurons (5, 6). In the end, the main effect is that you’ll feel more awake and less tired.

Digestive tract

Regarding the gastrointestinal tract, caffeine does not cause dyspepsia, a.k.a. upper abdominal pain. Caffeine-containing beverages can cause some reflux as it stimulates gastric acid secretion. (7). It’s unclear how caffeine alone affects bowel movements, e.g. peristalsis since there aren’t many studies on the topic. The most studied caffeine-containing beverage where bowel movements are concerned is coffee.  Colonic contractions can occur within 4 minutes of consuming coffee in some people, for others it can take a little longer but coffee is known to induce bowel movements. It’s likely that other aspects of coffee are involved though since decaffeinated coffee works as well (7).

Urinary tract

Some have suggested that caffeine increases the urgency to urinate. Some studies haven’t found an association between caffeine consumption and urinary incontinence (8). The Nurses Health Study and the Nurses Health Study II found a different result though. In those who consumed more than 450 mg of caffeine per day (more than 4 x 250 ml or 8 oz cups), a modest increase in frequent urgency incontinence was found (9). Caffeine stimulates the bladder muscles.

Circulatory system

Caffeine will cause a slight increase in heart rate that isn’t a problem for healthy individuals. Overall, caffeine doesn’t increase the risk of heart disease and may be beneficial for cardiovascular health when consumed within recommended amounts (10, 11, 12). Interestingly, there’s some evidence that caffeine may increase the risk for cardiovascular disease in so-called “slower metabolizers”, more on this below.


Caffeine may cause an insignificant rise in blood pressure, (e.g. about 3-4 mmHg) which tends to resolve in regular caffeine consumers (13, 14, 15, 16). Overall, regular caffeine consumption is not a causal effect for clinical hypertension (high blood pressure).

Respiratory system

Caffeine does increase breathing rate but relax, there’s nothing to worry about. As heart rate increases, breathing does too. This actually increases the amount of blood and oxygen that’s delivered to your body (including your brain). Caffeine is a bronchodilator meaning it dilates the passages in the lungs that air travels through. Bronchodilators also cause the respiratory muscles to relax – both of which create less resistance in the airways. This benefits both those without respiratory issues and those with, such as asthma.

Reproductive system

There isn’t any high-quality evidence that a modest level (< 300 mg/day) of caffeine consumption has adverse effects on fertility or pregnancy outcomes (17). Despite this, negative beliefs about caffeine and reproduction persist, and caffeine consumption is seen as an unhealthy habit. The American College of Obstetricians and Gynecologists recommend keeping caffeine intake to less than 200 mg/day to reduce the risk of miscarriage (18). Health Canada is a little less conservative, it recommends less than 300 mg/day.


There has been some research into the effects of caffeine on male infertility as it relates to sperm quality. Some suggestion has been made that caffeine may cause sperm DNA damage which may negatively impact male reproductive function. No studies have specifically looked at this so no conclusions can be made at this time; it remains speculative (19).


Tea with sliced lemon - Is Caffeine Bad For You?


Caffeine benefits

There’s a huge body of research looking at the effects (benefits and problems) of caffeine consumption, too many to list, but I’ve distilled some of the more popular ones I’m asked about routinely.

Improves mood

Caffeine releases dopamine and norepinephrine and is associated with lower rates of depression (20, 21, 22). Coffee and caffeine consumption is even associated with lower rates of suicide (23). But more isn’t necessarily better; a little goes a long way; second and third cups of coffee doesn’t increase observed benefits (24).

Improves brain function & memory

Caffeine can benefit brain function including short-term recall and reaction time, again through its action on dopamine and norepinephrine release (1). One study found that a 200 mg dose of caffeine increased memory performance in young adults (25) and caffeine in the morning may boost memory recall in the morning but not in the afternoon (26). Although not all research agrees, caffeine, in general, may help your brain function, function better (27).

Boosts glycogen replenishment

Caffeine can help to spare carbohydrate during exercise by increasing the amount of fat burned as fuel but also by helping store muscle carbohydrate (glycogen) from lasting longer (28, 29).

Enhances exercise performance

Intakes within the 400 mg per day limit (5 mg/kg body weight) were able to improve endurance when consumed about 1 hour before exercise (30). For some, 5 mg/kg might be a lot so it’s interesting to find other studies that showed similar exercise benefits with smaller amounts (3 mg/kg of body weight) (31). This exercise boost isn’t just for athletes, but for anyone who works out. It helps to reduce the perception of exertion so exercise feels easier; easier effort results in a better workout session  (32, 33).


Coffee wooden table - Is Caffeine Bad For You?


May boost metabolism

The idea here isn’t to pound back caffeine as a way to lose weight but caffeine can increase metabolic rate by 11% and fat burning by 13% (34, 35, 36). The effects are small and it may, or may not, make a difference over the long run (37, 38).

Reduces post-exercise pain

Research has shown that modest amounts of caffeine, about 250 mg, cut post-workout muscle pain by up to 48% in a small sample of volunteers (39). This may apply mostly to those new to exercise as they tend to experience the most soreness (Exercise Induced Muscle Damage).

Helps those with asthma

A review of 7 studies showed that caffeine opens airways and relieve bronchitis symptoms including wheezing, coughing, and breathlessness. Those with asthma found to benefit from caffeine’s airway-opening properties; allowing them to breathe easier. The effects are somewhat short-lived, lasting about 4 hours (40). To reap the benefit, you might need a couple of doses of caffeine throughout the day.

May improve Type 2 diabetes

Most of the studies looking at caffeine’s association with Type 2 diabetes have looked at coffee as the source. This is confounding as coffee contains lots of other organic acids and phytochemicals that might be responsible for the lower risk, and improved management of, diabetes as decaf coffee is also known to be beneficial (41, 42, 43, 44, 45). Genetics may play a role too regarding caffeine’s (coffee’s) impact on diabetes risk (46).

Caffeine safety

Caffeine is classified by the US Food and Drug Administration as “generally recognized as safe” or GRAS. This means qualified experts have assessed caffeine to be adequately shown as safe, under the conditions of its intended use.


In other words, when used as a food or medication additive or consumed as food within recommended limits, caffeine has not been shown to be a risk for human health. Obviously caffeine intake in children needs to be monitored. Energy drinks are not recommended for children given their high caffeine content.


Coffee cups five 1 - Is Caffeine Bad For You?


Caffeine overdose

The acute toxic level of caffeine consumption has not been established, but for adults, it’s about 10 g (10,000 mg) per day. This is the equivalent of 80 cups (250 ml or 8 oz) cups of coffee per day. It would be next to impossible to lethally overdose on caffeine from caffeine-containing beverages but that doesn’t mean caffeine is benign. Consuming a lot of caffeine in a short period of time (hint several large servings of coffee, energy drinks of caffeine pills) can result in arrhythmia and cardiac problems.


Documented cases of caffeine-related cardiac events involved high doses of caffeine taken in powder or tablet form, not beverages. Still, some coffee chains like Starbucks offer very large servings of coffee. A venti is 20 oz which, provides between 400 to 500 mg of caffeine in one sitting. The good news is, the average consumption of caffeine in most countries is well within safe levels. The cautionary tale is that even though caffeine is safe, problems can happen with overconsumption (1).

Symptoms of too much caffeine

Coffee and tea are very healthy beverages. As mentioned, caffeine’s safety is well demonstrated for the vast, vast majority of people when consumed in low-to-moderate amounts. However, high doses can be a problem. There are many caffeine effects to be aware of (47).

Caffeine side effects


Because caffeine stimulates the “fight-or-flight” hormone adrenaline (epinephrine) release, caffeine can increase the sense of, or aggravate anxiety (48). Intakes over 1000 mg (8 cups of coffee) can lead to nervousness, jitters, and a sense of panic (49, 50). The ‘a’ in adrenaline can be thought of as the ‘a’ in anxiety, anxiousness, aggravation, and even anger (irritation).


It goes without saying, too much caffeine can lead to sleeplessness and it can interfere with sleep quality (51, 52, 53).

Digestive issues

Some can’t tolerate caffeine and get loose stools when they consume it. Contrary to what you’ve heard, caffeine doesn’t cause ulcers (54). Caffeine can aggravate gastroesophageal reflux disease (GERD) (55, 56). Caffeine can cause gallbladder contraction which may explain why those with symptomatic gallstones tend to avoid coffee and caffeine-containing beverages.


Caffeine use disorder is recognized as a dependency disorder (more below). Some disagree that it’s a true addiction like alcohol, cocaine, or opioid use disorders are (57). For some, it’s really hard to break the caffeine habit, and while relying on a couple of cups per day for a little energy isn’t a problem, if you’re using caffeine to manage your life, because you get too little sleep, etc, then your consumption needs to be looked at.

High blood pressure

Caffeine does raise blood pressure, this isn’t disputed (58, 59, 60, 61). Caffeine’s effects on blood pressure are transitory and are initially strongest in caffeine naive people (a.k.a. “newbies”). It’s effects are greater when consumed in high doses or prior to exercise in sensitive individuals (62, 63). If you have clinically significant hypertension, best to moderate your caffeine intake and stay within recommended limits.

Coffee cartoon - Is Caffeine Bad For You?

Increased heart rate

The stimulatory effects of high caffeine intake may cause your heart to beat faster. Is susceptible people it can lead to atrial fibrillation or A fib (64). However, this effect doesn’t seem to occur in everyone equally. Even those with heart problems may be able to tolerate large amounts of caffeine without any adverse effects (65). Genetics likely plays a role too, slow metabolizers may be at great risk (see below). Like most things, gauge the effect for yourself.


This seems counter-intuitive given caffeine’s anti-fatigue, alertness-increasing properties. While caffeine increased alertness and mood post-consumption, one study found greater fatigue in subjects the next day (66). This is likely due to a rebound effect with can be avoided with daily consumption, within recommended levels of course!

Increased urination

Frequent urination is a common side effect given caffeine’s stimulatory effect on the bladder. The effects are mixed. In those with established urinary incontinence or urgency, caffeine’s effect is worse (67, 68). Regardless, increased urination does seem to be dose-dependent; the more caffeine you consume, the greater the need to pee (69).

Symptoms of caffeine withdrawal

Caffeine is technically a drug and according to the DSM IV Substance Dependence Criteria can meet the criteria for ‘addiction’.  Caffeine consumption is habit-forming. Many health professionals, including the World Health Organization, recognize caffeine use disorder and caffeine dependence (70).


There are a few different caffeine withdrawal symptoms to be aware of. The most common one is dubbed a caffeine headache.


The best way to avoid a caffeine withdrawal headache is to wean yourself off caffeine gradually. Reduce your intake by about half for 2 to 3 days and then reduce that amount by half again for a couple of days. After about 5 days or so, you can go completely caffeine-free if you want to without any concern for a headache.

Recommended doses

While there are no recommended intakes for caffeine as it’s not an essential nutrient, there are amounts of caffeine that are considered safe.

  • Adults: no more than 400 mg/day
  • Pregnant and breastfeeding women: no more than 300 mg/day
  • Children 12 and under: a maximum of 2.5 mg/kg of body weight, or about:
    • 45 mg/day for children 4-6 years (about one, 355 ml can of cola)
    • 63 mg/day for children 7-9 years (about one and a half 355 ml cans of cola)
    • 85 mg/day for children 10-12 years (nearly two, 355 ml cans of cola)

It doesn’t take much for children to reach these limits. A 12-oz (355 ml) can of cola has about 30 mg of caffeine and chocolate can have around 10 mg.

Coca Cola products - Is Caffeine Bad For You?

How long does caffeine last?

As long as it takes for your liver to breakdown and excretes it. When consumed as a beverage, caffeine enters the bloodstream immediately and starts to take effect within five minutes. You get an initial rush of dopamine and noradrenaline and a sensation of ‘aahh’. Caffeine levels peak in about 30 minutes.


On average, a healthy liver will take 5 hours to breakdown half the amount of caffeine consumed (a.k.a. ‘half-life’). If you had a double espresso at 7 am, half of the 80 mg of caffeine will still be in your system at 12 noon. Another medium-sized coffee at lunch would top up what’s in your system with another 200 mg.


It’s important to note that for higher doses of caffeine (250 to 500 mg), the clearance of caffeine is significantly reduced and caffeine’s half-life is prolonged. Given enough time, caffeine will be broken down and excreted. Caffeine does not accumulate in your body (1).


By 5 pm, you’d still have 20 mg from the espresso and another 100 mg from your lunchtime cup of joe for a total of 120 mg. Not bad, but if you’re consuming larger amounts of coffee or other caffeinated beverages and/or are consuming them more often, the caffeine starts to hang around. In this sense, it is possible to be ‘caffeinated’ for most of the day.

Impact of genetic makeup

Some studies have suggested that caffeine and coffee consumption leads to an increased risk of heart problems. How might drinking coffee lead to cardiovascular disease? Recent studies suggest that it goes beyond just stress hormones (cortisol and adrenaline).


The reason for these inconsistencies between studies could be due to genetic variation in the major caffeine metabolizing enzyme called cytochrome P450 1A2 (CYP1A2) (71, 72). CYP1A2 accounts for more than 95% of caffeine metabolism in the liver.


The activity of this gene influences how quickly your liver breakdowns (detoxifies) caffeine. No genetic mutation = “fast metabolizer”, genetic mutation = “slower metabolizer”. Because caffeine hangs around in the bodies of slow metabolizers’ longer, it can theoretically increase the risk for certain diseases like heart/cardiovascular disease.  There’s some evidence so to suggest that slower metabolizers should limit their intake of caffeine to 200 mg or less per day (71). You can do a saliva-based genetic test to see if what kind of metabolizer you are.


Slower metabolizers may experience increased effects of caffeine such as increased “nervousness” (73).


Dark chocolate - Is Caffeine Bad For You?

Caffeine content of various foods

There are several resources for the caffeine content of foods and beverages. Below are some of the more common sources:

    • 1 cup [250 ml or 8 oz] of brewed coffee = 125 mg
    • 1 cup [250 ml or 8 oz] of instant coffee = 76 – 106 mg
    • 1 cup [250 ml or 8 oz] of brewed tea = 45 mg
    • 1 cup [250 ml or 8 oz] of green tea = 30 mg
    • 1 can [35 ml or 12 oz] cola = 45 mg
    • 1 oz [30 ml ] espresso  = 40 – 60 mg
    • Red bull [250 ml or 8 oz] = 80 mg
    • Energy drinks such as Monster [500 ml or 16 oz] = 180 mg
    • Caffeine tablets (1) = 100 – 200 mg
    • Pain medications with caffeine = 65 mg/dose

Cutting back on caffeine

Many people who are used to having caffeine experience side effects like headaches and drowsiness when they suddenly stop taking it. Here are some tips to
cut back slowly:

  • Mix your regular coffee with half decaffeinated
  • Try caffeine-free herbal teas or apple cider for a hot
  • Choose a latte or café-au-lait instead of brewed
  • Brew tea for less time.
  • Try caffeine-free versions of your favourite
    carbonated beverages.

Bottom line

Caffeine has been part of the human diet for centuries.


Caffeine has been shown to have many health benefits such as improved brain function, reduced risk for Type 2 diabetes, better memory, improved mental health and mood, and reduced fatigue.


Like with all things, balance is needed when it comes to the effects of caffeine and how much you consume caffeine on a daily basis. Negative effects of excess caffeine consumption include anxiety, insomnia, reflux, possible increased high blood pressure, and cardiovascular disease in susceptible to people. Another possible negative effect of caffeine is a reliance on it to manage our ever-increasing busy lives and the demands placed upon us.


Caffeine can be enjoyed in amounts that bring pleasure to life while leveraging some of its beneficial properties while avoiding some of its negative effects. The key is to be armed with information including the common sources of caffeine found in foods, beverages, and medications and staying within official recommended guidelines where consumption is concerned.


Doug Cook RDN is a Toronto based integrative and functional nutritionist and dietitian with a focus on digestive, gut, mental health.  Follow me on FacebookInstagram and Twitter.