How does caffeine affect the brain?


I come across coffee every morning. There it is in my kitchen waiting to brighten my day. I’m a fan of the French Press Cafetiere although I’m not averse to going through the more religious experience of preparing my stove top, or Moka Pot, to give it it’s correct name, in order to give me my first caffeine experience of the day. The Moka Pot takes time and preparation giving it a ritualistic feel as you wait to mine the black nectar that is fuel for the mind and soul. 

However, coffee was no more than a drink to me until, as Sociology student, I read of the sociological meaning of coffee through the words of Anthony Giddens in his classic textbook ‘Sociology’ (1997). Coffee, he says, has symbolic value - it’s more than just a drink. ‘Let’s go for a coffee’, I often suggest to my friends who I know don’t even like coffee. But they instinctively know what I mean. Coffee fosters social relationships and also economic ones. In the UK alone the coffee industry saw a turnover of £1.5 billion in 2018 (Centre for Economics and Business Research 2018). This social and economic development has a rich history although the origins of the first coffeehouse appear to be disputed – was it Oxford, or was it London? One thing we do know, however, is that its origins date back to the middle of the 17th century. Oxford’s Queen’s Lane Coffee House is still in existence today over 350 years since its inception, although it has moved location. 

Another thing we now know is that coffee also contains a drug - caffeine.

Matthew Walker (2017) says that coffee consumption ‘represents one of the longest and largest unsupervised drug studies ever conducted on the human race’ (p.27,28). Surely then it is worthy of exploration – especially as  society generally views unsupervised drugs with grave concern. Caffeine however,  is not just in coffee. It’s in black tea, green tea, soft drinks energy drinks, and is also still present, in small amounts, in some decaffeinated drinks. You can therefore be surprised by a caffeine hit as it’s not always apparent you’re consuming it. Up to 400 milligrams (mg) of caffeine is usually considered a safe level of consumption and, to put this into perspective, one cup of brewed coffee contains about 100 mg (Mayo Clinic 2020). So that’s about four cups of my French Press Cafetiere coffee per day. Obviously, this depends on how strong you brew your coffee and the type of coffee you use. So, you can see how easy it is to go above the recommended limit’

Most of us, I’d hazard a guess, use coffee to give us a kick-start in the morning and to keep us going when we feel tired in the afternoon. So what is caffeine doing inside our brains to achieve this effect? 

Caffeine disrupts the ability of a chemical called adenosine to latch on to receptors in your brain. Adenosine’s job is to create an effect called ‘sleep pressure’. The amount of ‘sleep pressure’ you feel determines how sleepy you feel. You can probably recall feeling sleeps like this an hour or so after lunch. However, the caffeine stops this chemical effect by latching on to the receptors instead. The problem is, the adenosine in your brain continues to accumulate just waiting for its chance to seize back control. Therefore, once your body has removed the caffeine, using enzymes in your liver, the adenosine rushes in and you get that almighty mid-afternoon caffeine slump. So, to offset this, what do we often do? Drink more coffee! (Mordue et al 2020)

The problem with this, especially if it is late in the day, is that it may disrupt our ability to get to sleep. The term ‘half-life’ in relation to drugs refers to the length of time it takes the body to remove 50 per cent of the drug from your body. The half-life of caffeine can be up to 7 hours. The late afternoon ‘pick-me-up’ you have at 3 p.m. is therefore still in your system by 10 pm that evening. The effect of this is that you can’t sleep, meaning you’re likely to stay up late and miss out on the eight hours sleep you need – meaning that you reach for the coffee pot in the morning to get you started (Walker 2017).

But what about that ‘kick start’, that energy boost. What’s happening there and what exactly is the impact on our brains and therefore on our functioning? Moderate consumption of caffeine has been shown to improve attention, speed up reaction times, improve memory, improve verbal reasoning and improve our attention to the environment. However, in a study of college students, it was also shown to impair, or have little influence over some cognitive tasks (Curran and Marczinski 2017). Foxe (Foxe et al 2012) and colleagues noted the same. Caffeine, they reported, has repeatedly been shown to improve sustained attention, reduce error rates in pieces of work, and shorten reaction times. Crucially though these improvements were seen at the 50 mg level of caffeine consumption -  that’s about half a cup of my cafetiere coffee. It is clear, from the results of  most studies, that dose plays a crucial role and Curran and Marczinski point out that the best results are shown in people who are already fatigued. 

One interesting factor to consider is whether we are using caffeine to offset the trials of life? To look at it another way, if we lived a different sort of life would we need to be so wedded to our beloved caffeine?

Another problem with caffeine is that it’s addictive. If you’ve ever tried to go ‘cold-turkey’ and just stop drinking it you will have encountered some unpleasant symptoms. Caffeine withdrawal starts within less than 24 hours. Once we stop ingesting caffeine, our blood vessels widen, and blood flow is increased to the brain. This initially causes headaches which will settle down once the brain adapts to the increased blood flow (Merideth et al, 2009). If you are planning to reduce your caffeine consumption, then it is best to do it gradually or maybe take a ‘no caffeine after lunch’ approach. This can give you the benefits of caffeine without some of the associated problems. 

Once we’re hooked there are potential problems in over consumption. NASA repeated a 1940’s experiment in the 1990’s to explore the impact of a range of psychoactive drugs on spiders and the results were fascinating. They gave spiders a dose of a particular drug, in some cases marijuana or amphetamine and observed the webs that the spiders spun. They also gave some spiders a dose of caffeine. The results were alarming. In all bar the spiders that had ingested caffeine, the webs spun resembled a usual spider’s web. In the case of the caffeinated spiders,, the webs were random and largely unrecognisable as the concentric patterned webs we are used to seeing. Of course we are not comparing like-for-like, we have little in common with spiders. But this experiment does demonstrate the impact of caffeine compared to other drugs that most of us wouldn’t even entertain consuming. Some people’s central nervous system can become overwhelmed with too much caffeine, which can lead to scattered thinking, anxiety and restlessness. Much like the spiders.

Although I have focussed here on the impact on the brain it is worth noting the physical effects of caffeine that can include heart arrhythmia and high blood pressure. One of the problems, as with any drug, is that you become used to the effect so need more to achieve the same results and, while some of the physical problems are temporary, over consumption could cause problems for people already at risk of physical conditions. Those with any sort of heart problem should probably limit caffeine intake (McCusker et al, 2006, Spritzler 2017). 

Caffeine in many ways is embedded culturally through its inclusion in beverages that are part of our psyche. The coffee or tea break, the coffee shop, the ‘do more with the time I have’ energy drink culture, and the desire to squeeze more productivity out of our day. But it might actually be working against us. There appears to be an optimum level that does promote benefits for our brain in terms of attention and focus, but these dissipate at the levels that I’d suggest many of us consume caffeine at. If we go over this optimum level we are likely to experience scattered thinking, agitation, anxiety, rambling speech and excitement (Lu 2015). 

Moderation in everything, as my mother always advocates, seems to be the best approach. A good cup or two would seem to give us the benefits without the potential problems. 

So, how can we reduce our caffeine intake?Read the label and be vigilant for hidden caffeine in drinks and food.

  • Keep a diary of how much caffeine you consume – it might turn out to be more than you think.
  • Cut back gradually to avoid withdrawal.
  • Avoid caffeine in the afternoon and evening.
  • Check medicine ingredients as lots of medication, cold remedies for example, include caffeine
  • Go for decaf coffee – but remember decaf is not nocaf.
  • Shorten the brew time of coffee and tea or maybe go herbal! Remember Green Tea also includes caffeine



Curan, C. P. and Marczinski, C. A. (2017) Taurine, caffeine, and energy drinks: Reviewing the risks to the adolescent brain Birth Defects Research. 2017;109:1640–1648.

Foxe, J. J., Morie, K. P., Laud, P.J., Rowson, M. J., de Bruin, E. A. & Kelly S. P. (2012) Assessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention task Neuropharmacology 62 (2012) 2320e2327

Giddens, A. (1997) Sociology (3rd ed.) Cambridge: Polity Press

Lu, S. (2015) Too much coffee? American Psychological Association 28th October 2020)

Mayo Clinic (2020) Caffeine: How much is too much? (accessed 28th October 2020)

McCusker, R.R., Fuehrlein, B., Goldberger, B.A., Gold, M.S. and Cone, E.J. (2006) Caffeine Content Of Decaffeinated Coffee in Journal of Analytical Toxicology (2006) Oct;30(8):611-3.

Merideth, A, Addicott, L, Yang, A M, Peiffer, L R, Burnett, J H, Burdette, M Y, Chen, S H, Kraft, R A, Maldjian, J A and Laurientia, P J (2009) The Effect of Daily Caffeine Use on Cerebral Blood Flow: How Much Caffeine Can We Tolerate? Human Brain Mapping, 30(10): 3102–14.

Mordue, S. J., Watson, L & Hunter, S. (2020) How to Thrive in Professional Practice St.Albans: Critical Publishing

Walker, M (2018) Why We Sleep. London: Penguin Random House.


Stephen Mordue is a Senior Lecturer in Social Work at the University of Sunderland and author of 'How to Thrive in Professional Practice'. He was a social work practitioner and manager for 12 years working mainly with older people and their families. His areas of special interest are effective communication, and self-care and productivity for professionals. You can hear Stephen speak on self care at our online event: Self regulation for practitioners.