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What Time Should You Stop Drinking IRN-BRU Before Bed?

Last-call times for IRN-BRU computed from its sourced caffeine content and the 5-hour median half-life.

TL;DR

A 330 ml can of IRN-BRU carries 30 mg of caffeine, already under the 50 mg threshold where most people can fall asleep normally, so one serving needs no cutoff time. Multiple servings still stack: the median caffeine half-life is 5 hours.

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IRN-BRU Last-Call Times by Bedtime

Latest time to finish a 330 ml can of IRN-BRU (30 mg of caffeine) and still be under 50 mg of residual caffeine at bedtime, assuming the median 5-hour half-life. Your personal half-life may sit anywhere in the 2 to 12 hour range.

BedtimeLast call for IRN-BRUResidual at bedtime
9:00 PM (21:00)Any time30 mg (already under 50 mg)
10:00 PM (22:00)Any time30 mg (already under 50 mg)
11:00 PM (23:00)Any time30 mg (already under 50 mg)
12:00 AM (00:00, midnight)Any time30 mg (already under 50 mg)

Clearance Time by Serving Size

How long each serving of IRN-BRU needs before bed to drop under 50 mg:

ServingCaffeineTime needed before bed
330 ml can30 mgNo wait needed

Source: caffeine figures from IRN-BRU official FAQ, accessed 2026-06-11. Values can vary by batch, location, and preparation; check the label or the source for the latest figures.

How the Math Works

With 30 mg per 330 ml can, a single serving of IRN-BRU never crosses the 50 mg threshold where caffeine measurably delays sleep for most people, so there is no last-call time to respect for one serving. That changes when servings stack: caffeine decays exponentially with a median 5-hour half-life, so two or three servings through the afternoon and evening can still leave more than 50 mg in your system at bedtime.

Individual half-lives also run from about 2 to 12 hours depending on CYP1A2 genetics, medications, smoking, and pregnancy. If you are caffeine-sensitive or drinking multiple servings, model your real intake in the caffeine half-life calculator.

Related Guides

Half-Life CalculatorPersonalize the cutoff to your metabolism Caffeine in IRN-BRUEvery serving size, sourced All Sleep CutoffsLast-call times for 100+ drinks Caffeine and SleepThe science of timing your last cup

Frequently Asked Questions

There is no magic number, but around 50 mg of circulating caffeine the alerting effect fades for most people, which makes it a practical sleep-ready marker (the same one the Unbuzz app and our half-life calculator use). A 330 ml can of IRN-BRU starts at 30 mg, already below that mark, which is why a single serving needs no cutoff time. Caffeine-sensitive sleepers may need to aim lower; the calculator lets you change the threshold.
These times assume the median 5-hour half-life, but CYP1A2 genetics, oral contraceptives, pregnancy, some medications, and age stretch individual half-lives across roughly 2 to 12 hours. Even at a slow 8 to 12 hour half-life, the 30 mg in a 330 ml can of IRN-BRU starts under the 50 mg threshold, but stacked servings linger far longer for slow metabolizers, so spacing matters more. The caffeine half-life calculator adjusts the curve to your profile.
No. Per IRN-BRU official FAQ, the sugar-free variant has the same caffeine as the regular version, so the cutoff times above apply unchanged. Sugar affects the energy crash, not the caffeine clock.
Standard exponential decay: residual = dose x 0.5^(hours / 5), using the drink's sourced caffeine content (30 mg per 330 ml can, per IRN-BRU official FAQ) and the median 5-hour half-life. The last call is the latest time that leaves under 50 mg at bedtime, rounded down to 15 minutes so the rounding never works against your sleep.

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Medical Disclaimer: Caffeine values are approximate figures from the cited public sources. Actual content may vary by batch, location, and preparation, and caffeine metabolism varies widely between individuals. This page is for informational purposes only and is not medical advice. The FDA guideline for healthy adults is up to 400 mg of caffeine per day; the recommended limit during pregnancy is 200 mg per day. Consult a healthcare professional for personalized guidance.