Depending on your body, caffeine can either be your saviour or your enemy. Some people can’t get out of bed without their morning coffee or struggle to stay alert after lunch without a cup of tea. But while caffeine is a well-accepted (and frankly, delicious) part of normal routines, the energy buzz isn’t well digested by everyone. 

While you may be jealous of those who can get through the day without their caffeine fix, those who avoid the stimulant may be doing it not just for the bragging rights, but because they can experience some negative side effects from consuming it. 

Levels of caffeine peak in the blood within about 15–45 minutes of consumption. People notice the strongest effects during this time, either experiencing sudden bursts of energy or feeling jittery.

If you’re one of those people who has ever gotten the shakes after coffee or stomach issues after an espresso, it could be down to intolerance or sensitivity. Here’s how your body’s reaction to caffeine can determine if you’ve just one too many cups – or there’s a sign of a bigger problem at hand?

“Caffeine sensitivity and caffeine intolerance can be very closely linked,” explains dietician Catherine Rabess. “The desired effects of caffeine such as alertness and better concentration can become more easily and quickly heightened in those with higher sensitivity, but an intolerance indicates a negative effect, whether it’s a gastro-intolerance or other more marginalised effects on our bodies.” 

Symptoms of intolerance can present in those who drink above their tolerable threshold, or in those who have high sensitivity when trying even very small doses of caffeine. While the recommended safe dose for caffeine is up to 400mg of caffeine a day (around four cups of coffee), sensitivity differs from person to person. You may be classed as having a high sensitivity if you experience more severe responses to caffeine at doses lower than 400mg, and a low sensitivity if you can drink up to 400mg without noticing much impact. 

“People’s response to caffeine is very individualised,” says Catherine. “That’s usually based on genetic factors, so it’s actually in our DNA, and how our body functions.”

Catherine explains that our liver plays a big role in the metabolisation of foods and drinks – and how fast or slow the body metabolises caffeine will impact how sensitive you are to it. And the same can be seen with how quickly the stimulating effects of caffeine impact your central nervous system. “If you do have a slightly slower metabolism, that could mean that even small amounts of caffeine could cause more of a stimulating effect. Higher doses can then lead to heightened responses to caffeine,” Catherine says. 

If you have a caffeine sensitivity or intolerance, you may notice some of the following symptoms after having food or drink that include caffeine. 

• Insomnia 
• Anxiety
• Restlessness 
• High blood pressure 
• Functional gut issues, including IBS related symptoms
• Increased heart rate 
• Shaky hands
• Headaches

“The symptoms that can present are often very similar to other conditions, so it might actually be quite difficult to determine if that is a caffeine intolerance or if it is a mirror of other dietary issues or changes,” says Catherine. For example, you may experience these symptoms if you suddenly increase your caffeine intake, or they could also be a sign of withdrawal if you suddenly remove all caffeine from your diet.

It’s also important to remember that caffeine isn’t just found in tea and coffee, but also in fizzy drinks and some types of chocolate.    

“It’s hard to determine whether your response to caffeine is an intolerance without seeing a specialist in the area of dietary intolerances. If you have any of these symptoms there could also be other underlying issues, so always speak with your GP and get a referral to a dietician,” says Catherine.  

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