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Layer 3 — Inputs

Inputs: caffeine, alcohol, food, and exercise timing

What you put in and when shapes how you sleep — caffeine timing, the truth about a nightcap, and when to stop eating before bed. the night. Practical, evidence-led, no fearmongering.

Sleep supplement evidence tiers. Strong for a specific use: melatonin (circadian timing only). Reasonable evidence: magnesium glycinate, L-theanine, tart cherry. Promising but limited: glycine, apigenin or chamomile, ashwagandha. Popular but unproven: valerian, CBD, oral GABA. Doses and evidence ratings included; most sleep supplements are more hyped than proven.
Where each sleep supplement actually stands. Ranked by the honest weight of the evidence as of June 2026 — with typical doses. Educational, not medical advice.
Vertical timeline of caffeine remaining after your last cup, given a five-hour half-life: 0 hours 100 percent, 3 hours 66 percent, 6 hours 44 percent, 9 hours 29 percent, 12 hours 19 percent. Even nine hours later, enough remains to fragment early sleep.
Why an afternoon coffee follows you to bed. With a five-hour half-life, a 2pm cup is still a third active at 11pm. Stop caffeine eight to ten hours before bed.
Timeline of how alcohol affects sleep across the night: 0 to 1 hour faster onset, 1 to 4 hours REM and deep sleep suppressed, 4 to 6 hours fragmented sleep as alcohol clears, 6 hours plus REM rebound with vivid dreams and lighter sleep.
A nightcap costs you the back half of the night. Alcohol speeds onset but suppresses REM, then fragments the rest. Even moderate evening drinking lowers sleep quality.

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