Caffeine for Teens and Students in Exam Week: Official Limits and How to Protect Your Sleep

This is general information, not medical advice. Caffeine affects people differently, and some health conditions and medications increase sensitivity. Ask a doctor or pharmacist if unsure.

Many students lean on coffee, tea, cola or energy drinks during exam season. This article sets out what official sources actually say about limits for young people, what the evidence is on sleep, and what you can do to avoid the classic problem: caffeine that gets you through the afternoon revision session and then steals the night.

What the official sources say

FDA (United States). The FDA says that for most adults, 400 milligrams of caffeine a day is an amount not generally associated with negative effects. For young people, it says the American Academy of Pediatrics advises against energy drinks for children and teens, citing their sugar and caffeine content, and that too much caffeine in children and teens can cause sleep problems among other effects. It also notes that people differ widely in how sensitive they are to caffeine.

Health Canada. For children and adolescents up to 18, Health Canada's maximum is 2.5 mg of caffeine per kg of body weight per day. For adults it is 400 mg a day. Health Canada explains that it applied the child figure to adolescents because data on this group are limited, a precautionary approach, and notes that healthy older and heavier adolescents (14 to 18) may be able to consume caffeine in a similar manner to healthy adults. As arithmetic, 2.5 mg per kg works out to 150 mg for a 60 kg teenager.

UK. The UK government has announced that it intends to ban the sale of high-caffeine energy drinks (drinks other than tea or coffee with more than 150 mg of caffeine per litre) to under-16s in England from April 2027, subject to Parliamentary approval, citing effects on anxiety, sleep and concentration. The NHS advises drinking caffeine in moderation and notes that sensitivity varies.

Note that countries set different limits and these are not the same kind of document: some are population guidance, some are legal rules, and none is a personal prescription.

How much caffeine is in your drink?

The FDA lists wide ranges, which is why labels matter:

• Regular brewed coffee: 113 to 247 mg per 12 fluid ounces.
• Caffeinated soft drink: 23 to 83 mg per 12 fluid ounces.
• Energy drinks: 54 to 328 mg per 16 fluid ounces.
• Black tea: about 71 mg and green tea about 37 mg per 12 fluid ounces.

A single 12-ounce brewed coffee can therefore reach or pass the 150 mg example above. If you cannot find the number on the label, assume it may be high.

Where caffeine hurts exam preparation: sleep

In a placebo-controlled study in the home, published in the Journal of Clinical Sleep Medicine, a 400 mg dose of caffeine was taken at bedtime, 3 hours before bedtime, or 6 hours before bedtime. Each timing had a significant effect on sleep disturbance compared with placebo, and the authors said caffeine taken 6 hours before bedtime has important disruptive effects, supporting advice to avoid substantial caffeine for at least 6 hours before bed.

Caveats: 400 mg is a large dose, and the abstract does not say the study tested teenagers, so a small tea at lunch may have a smaller effect. A 2026 narrative review on adolescents reports that the strongest evidence links energy drink use with short or poor-quality sleep, but it is an association, and the review stresses that sugar-free products can still disrupt sleep through caffeine. The AASM and CDC both advise 8 to 10 hours of sleep for teens, so losing sleep to caffeine works against the thing you are trying to improve.

A cautious plan for exam week

These are practical suggestions based on the sources above, not medical advice.

1. Know your number. Check labels, and compare them with the limits for your age and body weight.
2. Do not change your habits on exam day. Keep to your normal amount, or none. The FDA lists jitters, palpitations, anxiety and upset stomach among effects of too much caffeine.
3. Set an early cut-off. Working from the 6-hour finding, if you go to bed at 10:30 pm, stop caffeine by about 4:30 pm. That is a conservative extrapolation, not a tested rule for teens.
4. Skip energy drinks. The FDA says experts advise against them for children and teens.
5. If caffeine makes you anxious, cut it down. The NHS student stress guide lists avoiding lots of caffeine among its tips for managing stress.
6. Do not use caffeine to replace sleep. If you are tired every day, the fix is sleep, not another cup.

Key takeaways

• FDA: 400 mg a day for most adults; experts advise against energy drinks for children and teens.
• Health Canada: 2.5 mg per kg per day for under-18s, applied to adolescents as a precautionary approach.
• Caffeine 6 hours before bed still disturbed sleep in one study at a 400 mg dose.
• Keep your routine the same on exam day.

For a full comparison of drinks and a worked example, see energy drinks vs coffee before exams. For what to do after a short night, read how to function after a sleepless night, and for test-morning food, what to eat the morning of an exam.

Sources

• FDA: Spilling the Beans, How Much Caffeine Is Too Much? - 400 mg for most adults, energy drinks and teens, effects, caffeine content table.
• Health Canada: Caffeine in foods - 2.5 mg per kg for children and adolescents, adult 400 mg, adolescents 14 to 18 note.
• GOV.UK: Children's health further protected with energy drinks ban - planned ban for under-16s in England, 150 mg per litre threshold.
• Drake et al., Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed (JCSM, 2013) - study abstract.
• Energy Drink Use and Adolescent Sleep Debt (Nutrients, 2026) - narrative review abstract.
• CDC: About Sleep - 8 to 10 hours for ages 13 to 17.
• AASM consensus statement on pediatric sleep (JCSM) - 8 to 10 hours for ages 13 to 18.
• NHS: Water, drinks and hydration - caffeine in moderation, sensitivity varies.
• NHS: Student stress self-help tips - avoid lots of caffeine.