David Saunders
If you’ve ever wondered how much coffee is bad for driving, you’re not alone—and it turns out plenty of UK motorists are guessing. A new study from car insurance expert MoneySuperMarket suggests caffeine is practically a co-driver for many of us, but safe limits are poorly understood.
As winter’s dark mornings and early nights bite, the research found more than a third of UK drivers (37%) reach for a caffeinated drink before setting off, while nearly 44% stop mid-journey for a caffeine boost. Caffeine may feel like the hero of the commute, but the numbers hint at a less glamorous truth: many drivers don’t know where the “helpful” line ends and how much coffee is bad for driving begins.
Caffeine is common—clarity isn’t
The study highlights a big knowledge gap around recommended intake. Scientific reviews consider up to 400mg of caffeine per day safe for adults, yet only 10% of drivers knew this, and 33% were completely unaware of it. In other words, plenty of people are fuelling up without a dashboard telling them when they’re nearing the red zone—hardly ideal when you’re trying to stay sharp at 70mph.
| Rank | Caffeinated drink |
|---|---|
| 1 | Instant coffee |
| 2 | Tea (English breakfast) |
| 3 | Caffeinated soft drinks |
| 4 | Green tea |
| 5 | Energy drinks |
| 6 | Latte (hot) |
| 7 | Americano |
| 8 | Flat white |
| 9 | Espresso |
| 10 | Iced latte |
And here’s the seasonal twist: two in five (41%) drivers said they drink more caffeine when limited-time drinks are on the menu. Festive flavours may be fun; your nervous system may disagree.
So… how much coffee is bad for driving? Start by counting the milligrams
The research points to a simple problem: caffeine content can stack up fast—especially with energy drinks and larger café orders.
- Energy drinks led the high-caffeine table, with a large 473ml can of Bang Energy containing 300mg of caffeine—75% of the recommended daily amount in one hit.
- A single can of Diet Coke accounts for 11% of the daily amount. The study found 10% of drivers say they drink four or more per day, landing at nearly half (44%) of the recommended intake from Diet Coke alone.
- A grande (medium) pumpkin spice latte comes in at around 185mg—almost half the daily guideline (46%).
So if you’re asking how much coffee is bad for driving, the unglamorous answer is: it depends less on the “coffee” label and more on the total caffeine you’ve piled up across the day—and whether you’re heading into the slump that can follow.
The caffeine “crash” drivers are feeling
Caffeine can support alertness, energy and concentration, but too much can backfire into what’s commonly described as a caffeine crash—a sudden drop in energy, mood and focus when the effects wear off.
MoneySuperMarket partnered with pharmacist Deborah Grayson, owner of Practice with Confidence, who explained what’s happening in the brain:
“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.”
That matters on the road because feeling wired isn’t the same as being in control. In fact, when asked about caffeine’s impact behind the wheel, almost three in ten (28%) drivers said they’ve felt jittery, shaky or “on edge” after caffeinated drinks—effects commonly associated with overdoing it.
“No legal limit”—but that doesn’t mean no risk
MoneySuperMarket’s car insurance expert Alicia Hempsted summed up the tricky part: caffeine isn’t illegal, but the consequences of misjudging it can still be costly.
“As caffeine isn’t classified as a controlled or restricted substance, there is no legal limit on how much drivers can consume before they drive.
“However, with some drinks now offering three-quarters of an adult’s daily recommended amount in one drink, drivers should be conscious about how much they consume, especially if they’re heading out on a long journey.
“Driver fatigue plays a part in around 20% of serious road accidents, so it’s vital to manage your alertness safely when on the roads.
“If fatigue from a caffeine crash affects driving performance or contributes to an accident – even a minor one – it could impact your insurance costs and no claims discount.
“The Highway Code advises taking regular breaks – ideally every two hours – and avoiding late-night journeys between midnight and 6 am when alertness naturally dips. Staying hydrated and planning rest stops can make a big difference to your safety.”
Practical takeaways for drivers
If the question in your head is still how much coffee is bad for driving, here’s the sensible, old-school approach: don’t rely on a “buzz” to keep you safe.
- Track your caffeine total across coffee, tea, soft drinks and energy drinks (it adds up faster than you think).
- Beware the post-caffeine dip—especially before long motorway stretches.
- Plan breaks (every two hours is the Highway Code guidance).
- Don’t try to “out-caffeine” tiredness—fatigue is fatigue, and the body eventually collects its debt.
Read the full Caffeine and Driving Report on the MoneySuperMarket website.
