People who rely on drinking tea, coffee and other energy-boosting drinks that contain caffeine should be aware of when the next cup could send them over into a toxic state. Most people believe that a few cups do little harm, but they can cause issues with your heart, cognitive function, and more.

The UK caffeine limit is up to 400mg per day for most healthy adults, based on advice from the European Food Safety Authority (EFSA). This is about four or five cups of tea or coffee. As Dr Tim Mercer pointed out, pregnant women should have no more than half of this amount (meaning 200mg per day).

Dr Mercer said: "A regular cup of coffee at home, an instant coffee, might be around about 100mg. You could have three or four of those. A cup of tea, if you don't leave the tea bag in too long, has somewhere between 50 and 80mg - so you can have a few more cups of tea than coffee."

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The practising GP goes on to say that certain energy drinks range from 80mg to 160mg, and overdoing it could lead to a state of "caffeine toxicity". He explained that this can lead to some "harmful symptoms" that take over your body in a number of ways.

For example, it can cause your heart to "feel like it's racing", increase anxiety and lead to "poor decision making". Physically, overdoing it on caffeine can increase a person's urge to go to the toilet, as well as trigger issues like acid reflux and heartburn.

Dr Mercer added: "There is a dark side to caffeine, that is, it's a 'drug'. It is dependency-forming, and many people start out feeling like they have a coffee in the morning, and they feel more alert.

"Soon, it becomes needing a second coffee before you leave the house and then, eventually, maybe even needing a coffee before you leave work so that you can stay alert in the car on the drive home.

"This then starts the vicious cycle that many of you will recognise, where you have your last caffeinated drink too late in the day, and then there's still caffeine in your system when you're trying to get to sleep. You get to sleep late, you have to wake up early and you haven't washed out all of that adenosine overnight by sleeping properly."

Adenosine is a natural compound that builds up in the brain while you are awake and eventually promotes the urge to sleep. But, caffeine blocks adenosine from properly binding to receptors in the brain, preventing it from signalling the brain to slow down, whether it's early morning or late at night.

Looking to kick the habit can be hard, especially if you have reached a stage where your entire day depends on your next dose. Dr Mercer suggested one way that people should "never underestimate" - the placebo effect of a decaf.

People can get caffeine-free versions of most tea and coffee brands. Certain soft drinks also have versions that are caffeine-free too.