The UK runs on caffeine. Tea, coffee, energy drinks, chocolate — it is woven into daily life. For most people, moderate caffeine consumption is perfectly safe and even associated with some health benefits. But for a significant minority, caffeine triggers uncomfortable or even distressing symptoms — anxiety, racing heart, insomnia, and digestive upset. If you have ever wondered why your colleague can drink four espressos with no effect while half a cup leaves you jittery, the answer largely comes down to genetics and metabolism.
Caffeine sensitivity refers to how strongly and how long your body reacts to caffeine. It is not the same as caffeine allergy (which is extremely rare and involves the immune system). Instead, it describes a heightened physiological response to caffeine's stimulant effects.
Researchers broadly categorise people into three groups based on how they metabolise caffeine:
Your caffeine sensitivity is primarily determined by the CYP1A2 gene, which produces the liver enzyme responsible for metabolising about 95% of consumed caffeine. People carry one of two common variants:
Research published in the New England Journal of Medicine and other journals has shown that slow metabolisers may face increased cardiovascular risk from high caffeine intake, while fast metabolisers appear to be protected. This underlines why generic caffeine advice does not work for everyone.
If you are sensitive to caffeine, you may experience some or all of the following symptoms — often at doses that most people would consider small.
The NHS notes that caffeine can worsen anxiety symptoms. If you have been diagnosed with an anxiety disorder or experience panic attacks, reducing caffeine intake is one of the first lifestyle changes commonly recommended. Even if you do not have a formal anxiety diagnosis, tracking whether your anxious feelings correlate with caffeine consumption can be revealing.
Understanding exactly how much caffeine is in your diet is the first step to managing sensitivity. Many people underestimate their total daily intake because caffeine is present in more foods and drinks than they realise.
| Source | Typical Serving | Caffeine Content |
|---|---|---|
| Filter coffee | 250ml mug | 90-140mg |
| Espresso | Single shot (30ml) | 60-80mg |
| Instant coffee | 250ml mug | 60-80mg |
| Black tea | 250ml mug | 40-70mg |
| Green tea | 250ml mug | 25-50mg |
| Matcha latte | 250ml | 60-70mg |
| Cola | 330ml can | 32-42mg |
| Energy drink | 250ml can | 75-80mg |
| Large energy drink | 500ml can | 150-160mg |
| Dark chocolate (70%+) | 50g bar | 25-40mg |
| Milk chocolate | 50g bar | 10-15mg |
| Decaf coffee | 250ml mug | 2-15mg |
| Hot chocolate | 250ml mug | 5-15mg |
Source: EFSA Scientific Opinion on caffeine safety; NHS Choices; British Coffee Association
Beyond the obvious cups of coffee and tea, caffeine appears in several places you might not expect.
Several over-the-counter medications sold in the UK contain caffeine as an active ingredient. These include some headache and migraine tablets (such as Anadin Extra, which contains 45mg per tablet), cold and flu remedies, and some weight-loss supplements. Always check the active ingredients list if you are sensitive to caffeine.
An important point for highly sensitive individuals: decaf coffee still contains 2-15mg of caffeine per cup. If you react to very small amounts, even decaf may cause symptoms. True caffeine-free alternatives include herbal teas (rooibos, peppermint, chamomile), fruit teas, and hot water with lemon.
Because caffeine affects people so differently, tracking your personal intake and reactions is the most practical way to find your safe limit.
After tracking for 2-3 weeks, look for patterns. You may find that:
NutraSafe can help you log your caffeine intake alongside your meals and track any symptoms, making it straightforward to identify your personal patterns and safe limits.
Once you understand your sensitivity level, there are several practical strategies for managing it.
If you need to cut back, do it gradually. Stopping caffeine abruptly can cause withdrawal symptoms — headaches, fatigue, irritability, and difficulty concentrating — that typically last 2-9 days. The NHS recommends reducing by about one cup per day over a week or two.
Some medications can slow caffeine metabolism, effectively making you more sensitive. These include certain antidepressants (fluvoxamine), the contraceptive pill, some antibiotics (ciprofloxacin), and the heartburn medication cimetidine. If you have recently started a new medication and notice increased caffeine sensitivity, discuss this with your pharmacist or GP.
The NHS recommends a maximum of 400mg of caffeine per day for healthy, non-pregnant adults (roughly 4 cups of filter coffee). Pregnant women should limit intake to 200mg per day. Children under 12 should avoid caffeine entirely, and teenagers should limit intake. If you experience persistent palpitations, chest pain, or severe anxiety after consuming caffeine, speak to your GP.
NutraSafe helps you log meals, drinks, and snacks — including caffeine sources — and track how they make you feel, helping you find your personal safe limit.
Download Free on the App StoreCommon caffeine sensitivity symptoms include anxiety and jitteriness, heart palpitations or rapid heartbeat, insomnia or disrupted sleep (even from morning coffee), digestive issues (stomach pain, diarrhoea, acid reflux), headaches, dizziness, and excessive sweating. Sensitive individuals may experience these symptoms from amounts that most people tolerate without issue — sometimes as little as 50mg (about half a cup of coffee).
Caffeine sensitivity is a heightened response to caffeine's stimulant effects — your body metabolises it more slowly, so the effects are stronger and last longer. A true caffeine allergy is extremely rare and involves the immune system, causing symptoms like hives, swelling, or difficulty breathing. Most people who "react badly" to caffeine have sensitivity, not an allergy.
The NHS and EFSA recommend no more than 400mg of caffeine per day for healthy adults — roughly equivalent to 4 cups of filter coffee or 5 cups of tea. Pregnant women should limit intake to 200mg per day. However, people with caffeine sensitivity may need to stay well below these limits. Your personal tolerance depends on genetics, medications, and other factors.
Caffeine sensitivity can change over time due to several factors: hormonal changes (pregnancy, menopause, menstrual cycle), certain medications that slow caffeine metabolism (some antidepressants, contraceptive pills, antibiotics), reduced liver function, increased stress or anxiety, ageing (the body metabolises caffeine more slowly with age), and changes in sleep patterns.
Beyond obvious sources like coffee and tea, hidden caffeine is found in dark chocolate (up to 80mg per 100g), green tea and matcha, cola and energy drinks, some medications (pain relievers, cold remedies), decaffeinated coffee (still contains 2-15mg per cup), chocolate-flavoured foods (ice cream, biscuits, cereals), and some protein bars and pre-workout supplements.
Explore more tools and guides for tracking food reactions:
Last updated: February 2026