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How does caffeine affect performance?


Picture of a cup of coffee

Jake Lovelock is one of the Psychologists at Cognacity and is currently preparing for a 24-hour run.

As part of the race, he’s helping some fellow competitors with their mental preparation.

Questions about caffeine are some of the most common questions he’s received in recent months, whether in relation to my event or from clients and patients in relation to their general mental health and performance. Many of us have heard about the positive effects of caffeine. In fact, many of us could hardly perform without it. This is all well and good, but any psychoactive substance can (and should) bring up questions about long term changes to brain function, optimal and suboptimal doses etc.

In this blog, he’s collated all the questions he’s received in relation to caffeine. He have deliberately kept his answers brief, and summarised the current state of the literature (you’ll see very little is conclusively known about caffeine). If you’d like more information, have found some conflicting evidence or simply want to chat through things, feel free to drop him an email on

How does caffeine improve performance?

There are a couple ways caffeine improves performance. Firstly, as you burn energy throughout the day, a by product called ‘adenosine’ is created. Your brain can gauge how much energy we have expended over a period of time by how much adenosine has built up.

Caffeine’s first role is to bind to the adenosine receptors, which prevents our brain from seeing how much adenosine has built up, therefore delaying our perception of how tired we are (Ribeiro & Sebastiao., 2010).

Caffeine also increases the circulation of epinephrine and norepinephrine – both of which play a role in the ‘adrenaline rush’, it increases accessibility to sugars, redirects blood flow to major muscle groups and increases our heart rate to improve our performance (Soeren, Mohr, Kjaer and Graham., 1996).

There have even been studies showing benefits of caffeine in fat oxidation (Gutiérrez-Hellín et al., 2018), appetite suppression, increases body’s production of heat (thus increasing calorie expenditure) (McHill, Smith & Wright Jr., 2014).

In short, caffeine makes energy more readily available in our body, and for a period of time tells our brain to ignore how tired we are.

Why is caffeine so addictive?

Long before we started using caffeine, plants were producing caffeine for their own use. Plants used caffeine to help pollinators (i.e., bees) remember where to find them amongst all the other plants (by improving memory) and reward interacting with them (by giving them a positive ‘buzz’!). (Wright et al., 2013)

We notice this same reward effect with caffeine. Caffeine itself actually has a quite bitter and uncomfortable taste, but through simple classical conditioning, your brain starts to enjoy the taste. This association can be paired with a huge number of foods or drinks to convince our brains that we enjoy the taste; it can even be paired with activities such as physical exercise to make us feel like we enjoy it more (For example, see Richardson, Robers & Elliman., 1996)

What are the short-term side effects of caffeine?

Aside from the ergogenic (performance improving) effects of caffeine, there are other side effects. Caffeine is a diuretic meaning it increases the production of urine, though depending on how caffeine is consumed, the dehydration effect may be counteracted by the liquid it’s taken with (Zhang et al., 2015).

If you consume too much caffeine (see the below for estimated optimal doses) it can cause anxiety, difficulty concentrating, headaches, elevated heart rate, restlessness, and shakiness (Boderick & Benjamin., 2004).

Caffeine also has a particularly troubling relationship with sleep, which we also have a section on below.

What are the long-term side effects of caffeine?

The longer-term effects of caffeine use are difficult to test. Such a large percentage of the population supplements with caffeine that researchers generally find it difficult to collect control groups.

A famous study with mice found that long term caffeine use may increase the number of adenosine receptors in the brain, potentially leading to greater sensitivity to fatigue, but those results haven’t been proven in humans yet and more recent research doesn’t seem to support this claim (Boulenger, Patel, Post, Parma and Marangos., 1983).

In fact, research doesn’t conclusively support any theories that suggest caffeine creates long term changes in brain function! A fantastic review by Lara, Ruiz-Moreno, José Salinero, Del Coso (2019) reviewed all evidence into caffeine tolerance, their statement on the subject is below:

“Thus, although there is a paradigm suggesting that habitual caffeine intake may influence the performance benefits derived from acute caffeine ingestion, the scientific literature does not support this notion.”

In their research, they found that caffeine habituated individuals still benefitted from the performance enhancing effects of caffeine, in some cases, more so than those who did not have the same caffeine tolerance. These findings, and many more suggest that caffeine tolerance, at least in the way we understand it, may not actually exist; and the changes in sensation over time may be us simply getting used the effects of caffeine.

What happens in my brain when I feel caffeine withdrawal?

When you consume caffeine regularly, there are lots of physiological changes that your body and brain start to get used to. Anytime you consume caffeine, blood vessels in your brain constrict. When drinking caffeine regularly, we become accustomed to this effect.

If you were you refrain from drinking caffeine for a period of time, blood flow to the brain would increase again. This blood flow increase feels unnatural to us, and can induce headaches as we get used to it. These headaches normally subside after a short period of time, but may be more intense if you’re used to greater quantities of regular caffeine use (Addicott et al., 2009).

You may also feel particularly tired when refraining from caffeine. When chronically using caffeine, our brains get used to being blocked off from the adenosine, and it can be quite a shock to the brain. There are claims that we become more sensitive to fatigue as we chronically use caffeine, though, as mentioned above, research to support those claims is limited.

Withdrawal can also lead to mood changes, difficulty concentrating and further feelings of anxiety.

How much caffeine should I be taking?

Recommended quantities for performance enhancement are between 3 and 6 milligrams per kilo of bodyweight in a single instance of caffeine consumption (Guest et al., 2021). Though, I would recommend you test out different quantities of caffeine. Research has found that even minor amounts of caffeine can lead to increased anxiety and decreases in performance for some, even in quantities lower than the recommended below, however that does apply to a minority. Those of us that are more caffeine adapted will be able to tolerate higher doses without those downsides.

If you are looking for quantities of caffeine to optimise your day to day, it may be wise to reduce the amount of caffeine you are consuming to 2-4mg per kilogram of bodyweight. There is limited evidence that we become adapted to caffeine use, which can reduce its performance enhancement, using a lower daily dose leaves the flexibility to increase consumption on high performance days and still receive strong ergogenic benefits (Addicott & Laurienti., 2009).

It is still unknown how the ideas ‘caffeine adaptation’ and the lack of support for ‘caffeine tolerance’ work together.

I have an endurance event (any event lasting longer than 12 hours) how should I manage my caffeine intake accordingly?

These longer events often require a lower intensity over a much longer period of time, which means we may not need the performance enhancing benefits of caffeine from the beginning of the event. There are promising data that suggest using caffeine in response to periods of mental fatigue during these challenging endurance events may be advantageous (Azevedo et al., 2016).

This means that during endurance events we can respond to periods of mental fatigue or challenge with caffeine to boost performance, for example, taking or increasing caffeine consumption for your turn to speak during a conference or when it gets dark during an ultra-event.

How long does it take for caffeine to kick in?

Caffeine starts to be absorbed into the system almost immediately after being consumed, and caffeine in the bloodstream continues increasing until peaking between 45 and 60 minutes after consumption.

However, there are a couple variables affecting how quick caffeine kicks in. If you’ve recently eaten, it may take longer for caffeine to peak in your system. Method of consumption also affects uptake. For example, caffeine gum is significantly faster acting than other sources of caffeine.

What are some example sources of caffeine?

Teas, coffees, energy drinks even chocolate has caffeine in it. Depending on the ingredients in your particular source, there can be dramatically varying quantities of caffeine. Many don’t know that chocolate has caffeine in it! I would always recommend reviewing the caffeine source you personally enjoy.

For example, your ‘average’ cup of coffee has about 80mg of caffeine, but a ‘Venti Blonde Roast Coffee’ contains approximately 475mg of caffeine. For more information on caffeine sources, the website: has a full list of caffeine content in common sources.

How long does it take for caffeine to leave my system?

As a general rule, research suggests that caffeine has an approximate half-life of 5 hours. Which means that 5 hours after consuming caffeine, you’ll still have half of it in your body. Unfortunately, this isn’t a hard and fast rule for everyone, and research has found this half-life can range from person to person (Magkos, 2005).

Will caffeine negatively impact my sleep?

If we understand that one of the primary roles of caffeine is blocking of adenosine receptors (i.e., it blocks our brain from recognising how tired we are), then we could assume it isn’t going to be helpful for sleep!

There are two ways that people will commonly talk about their own sleep after consuming caffeine:

Case 1 – “My head hits the pillow, and I just can’t get to sleep. I stay in bed for hours before nodding off”

Case 2 – “I can have caffeine before sleeping and it doesn’t impact my sleep at all”

Unfortunately, caffeine will always negatively impact the quality of our sleep. There is clear variance in how much it impacts our sleep, for example, some individuals only need a small amount of caffeine to interrupt their sleep cycle, while others will be able to consume caffeine and only minorly impact the quality of their deep sleep. Nevertheless, having caffeine especially in the afternoon / evening will interfere with your physical and psychological recovery

Jake Lovelock, Performance Psychologist at Cognacity


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