When Should You Stop Drinking Caffeine?

The Problem with Generic Caffeine Advice

Most people follow a single rule: "No coffee after 2pm." This works for roughly 55% of the population. The other 45% — possibly including you — have a completely different caffeine metabolism.

Your CYP1A2 gene determines how fast your liver clears caffeine from your bloodstream. If you inherited the "slow metaboliser" variant, a coffee at 2pm might still have 80–100mg of active caffeine in your blood at 10pm bedtime. If you inherited the "fast metaboliser" variant, that same coffee is largely cleared by 5pm.

A five-hour difference. No wonder generic sleep advice doesn't work for everyone.

Caffeine Half-Life: The Core Concept

Caffeine's half-life is the time it takes your body to eliminate half of what you consumed. This follows first-order exponential decay — not a linear reduction.

What this means in practice

Say you drink a 200mg coffee at 3pm with a 10:30pm bedtime:

Why Caffeine Disrupts Sleep Even When You Feel Fine

Here is the insidious reality of habitual caffeine use: tolerance to caffeine's alertness effect builds much faster than tolerance to its sleep-disrupting effects.

If you're a regular coffee drinker, you may stop feeling the afternoon coffee after a few weeks. You think it's not affecting you. But research shows that even habitual caffeine users continue to lose measurable deep slow-wave sleep — they just don't feel the loss because they're adapted to functioning in a sleep-deprived state (Nehlig, 2018).

You don't feel the sleep loss. But it's still happening.

How to Find Your Personalized Cutoff Time

Your optimal caffeine cutoff depends on:

• Your CYP1A2 metabolism type — fast, normal, or slow clearance
• Your target bedtime — when you actually need to sleep
• The amount of caffeine you consumed — total mg matters, not just number of cups
• Your body weight — affects peak plasma concentration
• Your caffeine sensitivity — some people target <50mg at bedtime; sensitive sleepers may target <20mg

Not Sure of Your Metabolism Type?

You can estimate your CYP1A2 metabolism type using our Caffeine Sensitivity Quiz on the Tools page — a 6-question assessment based on how caffeine actually affects you. For a definitive answer, consumer DNA tests (such as 23andMe or AncestryDNA) include CYP1A2 genotype data in their raw downloads. Other consumer DNA services may also provide this data.

What to Drink After Your Cutoff

Once you've reached your caffeine cutoff time, water, decaf coffee, and herbal teas are straightforward alternatives. Water is always the safest option. Decaf typically contains 2–5mg of caffeine per cup — negligible for most people.

Note: specific health claims about herbal tea ingredients (chamomile, valerian, etc.) vary in evidence quality. We recommend them as zero-caffeine options, not as medically proven sleep aids.