Half-life of caffeine: how long it stays in the body

The half-life of caffeine in adults is around five hours on average. After this time, half of it has been broken down. How quickly this happens varies from person to person. Here you can read about when caffeine takes effect, what affects its half-life and how long before bedtime you should avoid it – with a calculation example and sources.

When does caffeine take effect?

Caffeine is absorbed quickly and completely after consumption. According to the Federal Institute for Risk Assessment (BfR), the effects can set in 15 to 30 minutes later and last for several hours. Caffeine is metabolised and broken down in the liver and excreted via the kidneys.

In detail: When taken orally, almost 100 per cent of the caffeine enters the bloodstream. The liver enzyme CYP1A2 metabolises it into paraxanthine, theobromine and theophylline, which are further broken down and excreted in the urine.

What ‘half-life’ means – a calculation example

The half-life is the time it takes for half of a quantity to be broken down. With a half-life of around five hours, a quarter remains after ten hours, and an eighth after 15 hours. Here’s how it works for a can of Energy – Blackcurrant & Pomegranate, containing around 106 mg of caffeine:

The table is based on an average of five hours. In healthy adults, the half-life varies considerably. Consequently, recommendations on how long before bedtime one should stop drinking range from 4 to 11 hours. After five half-lives, approximately 97 per cent has been broken down, according to the calculations.

What affects the half-life

• Smoking: In smokers, the half-life is up to 50 per cent shorter than in non-smokers.
• Pregnancy: Particularly in the final trimester, this can rise to as much as 15 hours. According to the EFSA, pregnant and breastfeeding women should not consume more than 200 mg of caffeine per day in any case.
• Medicines: As caffeine is metabolised by the enzyme CYP1A2, it may interact with medicines that are metabolised in the same way, including various psychotropic drugs. The EFSA has not established any safe levels of caffeine for people taking medicines. In such cases, please ask at your chemist’s or GP’s surgery.
• Habit: People who consume caffeine regularly may develop a tolerance. As a result, some of the usual effects may be less pronounced or may disappear altogether.

Where caffeine is found – and what’s left in the evening

The BfR provides these approximate values per portion; the caffeine content may vary:

Based on a half-life of five hours: if you drink a filter coffee at 4 pm, around 45 mg will still be in your body at 9 pm, and around 22 mg at 2 am. Anyone who drinks a can of energy drink – Blackcurrant & Pomegranate flavour – at 6 pm will still have around 53 mg in their body by 11 pm.

According to the National Consumption Study II, adults in Germany consume caffeine primarily through coffee, accounting for 85 per cent of their intake. According to the EsKiMo II study, young people aged 12 to 17 consume it mainly in the form of coffee (32 per cent), tea (30 per cent) and caffeinated soft drinks (20 per cent).

Caffeine and sleep: how long beforehand should you cut it out?

According to the EFSA, even single doses of 100 mg can affect sleep duration and sleep patterns in some adults, particularly shortly before going to bed. One serving of ‘Energy – Blackcurrant & Pomegranate’ contains around 106 mg, which is above this level.

A study by the Henry Ford Hospital in Detroit investigated how far in advance this affects sleep: twelve healthy adults with normal sleep patterns took 400 mg of caffeine at their usual bedtime, three or six hours beforehand. All three timepoints significantly disrupted sleep. Even when taken six hours beforehand, the caffeine reduced measured sleep by more than an hour. The researchers see this as supporting the recommendation to avoid large amounts of caffeine at least six hours before going to bed.

Important to bear in mind: The study was small and used a dose of 400 mg – the amount that the EFSA considers safe for healthy adults to consume over the course of a whole day.

What happens when quantities are high

The BfR states that high levels of caffeine can cause adverse effects such as nervousness, insomnia, sweating and palpitations. The severity of these effects depends on the dose and the individual’s sensitivity. According to the EFSA, up to 200 mg at a time and up to 400 mg spread throughout the day are considered safe for healthy adults. For children and adolescents, the limit is 3 mg per kilogram of body weight, either as a single dose or spread throughout the day. Our caffeine table shows how much caffeine is contained in coffee, tea, cola and energy drinks.

According to the BfR, anyone who suddenly stops consuming large amounts after regular, high consumption may experience withdrawal symptoms, such as headaches, tiredness and irritability. These typically begin 12 to 24 hours after the last intake, peak after one to two days and can last up to a week. Reducing intake gradually can help to avoid them.

Spotting caffeine on the label

Caffeine occurs naturally in coffee beans, tea leaves and cocoa beans. However, it is also isolated or produced chemically and added to products such as cola drinks, energy drinks, sweets, ice cream and baked goods.

Drinks containing more than 150 mg of caffeine per litre must carry the warning ‘High caffeine content. Not recommended for children or pregnant or breastfeeding women’, in the same field of vision as the product name and stating the caffeine content. Exceptions to this are coffee and tea, as well as coffee- or tea-based drinks that are named as such. ‘Blackcurrant & Pomegranate’ carries the warning with 32 mg per 100 ml.

Take care with pure caffeine powder: according to the BfR, just 0.2 g of powder is equivalent to 200 mg of caffeine – which is the single dose for healthy adults. It is not possible to measure this accurately using kitchen scales set to 1-gram increments – the risk of an overdose is high.

Rules of thumb

• You should expect a half-life of around five hours – it may be shorter or longer in your case.
• Avoid consuming large amounts of caffeine at least six hours before going to bed.
• A maximum of 200 mg at a time, 400 mg a day for healthy adults; 200 mg a day during pregnancy and whilst breastfeeding.
• Add up all sources: coffee, tea, cola, energy drinks.
• Children: avoid drinks with a high caffeine content.

Read more: How much caffeine a day? and Energy no sugar.

Frequently Asked Questions

Sources

1. Acqua Reaper: Product label for Energy Blackcurrant, as at 07/26.
2. NCBI Bookshelf / StatPearls (Evans J, Richards JR, Battisti AS): Caffeine, last updated 29 May 24. ncbi.nlm.nih.gov
3. Federal Institute for Risk Assessment (BfR): Questions and answers on caffeine and caffeinated foods, including energy drinks, FAQ dated 5 January 2026. bfr.bund.de
4. European Food Safety Authority (EFSA): Caffeine, Scientific Opinion 2015, accessed 16 September 2026. efsa.europa.eu
5. Journal of Clinical Sleep Medicine (Drake C, Roehrs T, Shambroom J, Roth T): Effects of caffeine on sleep when taken 0, 3 or 6 hours before going to bed, 2013;9(11):1195–1200. pmc.ncbi.nlm.nih.gov