Caffeine and Driving: The Hidden Risk to Road Safety
We've analysed how much caffeine is in popular drinks, and undertaken a study of 1,000 UK motorists to find out how aware drivers are of caffeine side-effects.
Key Takeaways
Only 10% of drivers know the recommended daily caffeine limit is 400mg
Nearly one in five drivers have experienced a caffeine-crash whilst driving
Over half of drivers aged 25-34 have felt ‘jittery’ and ‘on edge’ when driving after consuming caffeine
Whether it's a morning commute or the beginning of a road trip, millions of drivers reach for tea, coffee, or another caffeinated drink for an energy boost. But how effective is caffeine for drivers, and how often might we exceed the recommended daily intake without realising?
The effects of caffeine
Driver fatigue is one of the leading causes of road accidents, with tiredness estimated to play a role in up to 20% of serious crashes [1]. A little caffeine can help you feel more alert and focused. However, if you have too much, you might end up feeling jittery or restless, which could have consequences if you’re driving.
Even a minor accident can have an impact on your car insurance premium and affect your no claims discount. To explore the relationship between caffeine and driving, we asked drivers to self-report their daily caffeine consumption, how they feel about caffeine and how it affects their driving. We also analysed how popular caffeinated drinks might be pushing motorists over the recommended limit.
How clued up on caffeine are drivers?
When asked whether they knew the limits of the recommend daily caffeine amount, over two-fifths of drivers (45%) didn’t know the amount. Only around one in ten drivers (9.5%) were aware that the recommended daily caffeine limit for adults is 400mg [2].
The caffeine crash
A known side effect of drinking too much caffeine is the ‘caffeine crash’, which one in four (27%) drivers say they have experienced. This crash is caused when caffeine consumption delays the “tired” feeling many of us want to avoid, however once the caffeine effect wears off, your body can feel more tired than it might have felt otherwise.
Pharmacist and owner of Practice with Confidence, Deborah Grayson, who we partnered with for the research, said: “Caffeine wards off tiredness by blocking the neurotransmitter adenosine that builds up in the brain, making us feel sleepy.
“After the effects wear off you can feel less alert or focused, but if you feel extreme tiredness, problems concentrating, you’re irritable and you have a headache, that may indicate a caffeine crash.”
In terms of side effects, during a caffeine crash you might feel:
Sudden onset of fatigue
A drop in mood or becoming more irritable
Headaches
Mental fog
Decreased alertness
Slower decision making
Grayson continues: “Caffeine has an average half-life of five hours, but this is widely varied and depends on several factors including genetics, age and smoking. This means that it takes the body five hours to eliminate half the caffeine that you’ve consumed. “A crash can occur after as little as 30 minutes to three to six hours and will be worse with higher levels of consumption or when you’re already tired to start with.”
Caffeinated in the car
Over a third of drivers (37%) reported they have a caffeinated drink before they head off on a drive, whether it’s their morning coffee before they head into work, or grabbing an energy drink before a longer drive.
When asked about the impact caffeine has on them whilst behind the wheel, more than a quarter (28%) say they’ve felt jittery, shaky or “on edge” after drinking caffeinated drinks. Some drivers have experienced this more than others, with one in two (53%) 25–34-year-olds reporting they’ve suffered from these side effects whilst in the car.
Some drivers like to top up their caffeine levels whilst driving with over one in six (17%) sipping something on the go, whether it’s an energy drink or a takeaway coffee to help them feel more awake.
We also asked drivers who head out on longer journeys if they felt the need to stop specifically for a caffeinated drink, and four in 10 (44%) said they have made a stop just to top up on caffeine.
Asking drivers if they felt comfortable driving whilst feeling over-caffeinated, one in five (20%) shared they don’t. This could be because they felt jittery or “on edge” or because they felt a little out of sorts, so didn’t like the thought of being behind the wheel after consuming too much caffeine.
The caffeinated drinks drivers consume the most
Asking drivers which caffeinated drinks they consume the most, instant coffee topped the list as the firm favourite, followed by a classic cup of tea. Many drivers reach for these easy to make hot drinks first thing in the morning to help them feel more awake ahead of their commute to work or before they head out on a big drive.
Soft drinks are the third most popular caffeinated beverage people enjoy, such as a can of Diet Coca-Cola, which many use as an afternoon pick me up.
Lattes are another popular caffeinated drink with drivers, with both hot and iced versions making the top ten list. Interestingly, our survey revealed that seasonal offerings of this popular coffee, such as pumpkin spiced or gingerbread flavourings encourage drivers to drink more caffeine than they usually would, with two in five (41%) admitting to drinking more caffeinated drinks when they’re available.
When it comes to getting through the darker, gloomier winter months, almost half of the drivers surveyed (47%) said they tend to drink more caffeinated drinks. The colder weather encourages more people to pick up a caffeinated beverage, meaning it could be easier to exceed the recommended daily limit without realising.
The top 10 most popular caffeinated drinks drivers consume
Instant coffee
Tea (English breakfast)
Caffeinated soft drinks
Green tea
Energy drinks
Latte (hot)
Americano
Flat white
Espresso
Iced latte
Younger drinks most likely to be over-caffeinated
Younger drivers reported that they prefer to reach for caffeinated energy drinks. Whilst most drivers say they drink one of these a day, almost one in four (24%) 17–24-year-olds say they consume two a day, and one in six (15%) say they drink three energy drinks a day. With a lot of energy drinks containing extremely high levels of caffeine, in some cases up to 300mg, it means with just one drink, drivers are reaching 75% of their daily recommended allowance.
Most popular caffeinated drinks for young drivers (17–24-year-olds)
Energy drinks
Caffeinated soft drinks
Green tea
Iced latte
Instant coffee
Deborah Grayson explains: “Energy drinks not only have high levels of caffeine; they also often contain high levels of sugar and ingredients such as taurine that promise to boost alertness. “This leads to a combination of a sugar crash and a caffeine crash, which will only exacerbate the fatigue.”
Caffeine in everyday drinks: How much is too much?
It might come as no surprise to see energy drinks topping the list for the most caffeine, with a large can (473ml) of Rockstar Xdurance containing 300mg of caffeine, which is 75% of the recommended daily intake for adults. Couple this with a coffee in the morning, and a soft drink later in the day, drivers can easily exceed the recommended limit without realising.
Dunkin’ iced coffee is the most caffeinated coffee with a single cup providing almost three quarters (74%) of the daily recommended allowance.
A drink that has been everywhere this year, matcha, is also a popular caffeinated beverage. A Starbucks matcha latte contains 29% of the recommended daily amount.
Drinks you might not consider to be particularly caffeinated, such as soft drinks, can still add up and cause side effects, as one in 10 (10%) reported drinking four or more of these a day.
A closer look at coffee
Another popular coffee, the flat white can contain a high amount of caffeine, with a Costa flat white (299ml) delivering 60% (241 mg) of your daily recommended caffeine in one cup, that's .81mg of caffeine per ml, making it one of the strongest coffees on offer.
Methodology
Sources:
[2] https://www.fda.gov/consumers/consumer-updates/spilling-beans-how-much-caffeine-too-much
A survey of 1,000 UK drivers was conducted via Censuswide, all data correct as of October 2025.
Caffeine content for drinks taken from https://www.caffeineinformer.com/ and official brand websites.
UK driver estimates based on DVLA’s driving licence registrations last year: https://www.driving.org/record-high-uk-driving-licence-holders-soar/?utm_source=chatgpt.com
Deborah Grayson is a pharmacist with 30 years’ experience, and a nutritional therapist regarded as a leading expert in gut health. Deborah also runs Practice With Confidence, a groundbreaking academy which teaches transformative patient care, and is the pharmacist and nutritional therapist in residence for Heartburn Cancer UK.