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The Primary Zeitgeber

The single most powerful, most actionable circadian intervention. Get morning light.

ZeitgeberLight therapy FDA-cleared (SAD)

Adenosine · Sleep Pressure / Process S

The molecule that tracks how long you have been awake, and the one caffeine blocks to hide the bill.

Sleep NeuroscienceIV adenosine approved (Adenocard, 1989) for PSVT, not for sleep; no sleep indication exists

When You Eat vs What You Eat

The same meal eaten at night is metabolically worse than eaten in the morning.

MetabolismDietary timing science

The Hormone of Darkness

Not a sleeping pill, a darkness signal. And most people take 10x too much.

HormoneOTC supplement (US); Rx in EU

The Evidence-Based Morning Routine

Consistent wake time, morning light, then everything else. The highest-yield routine there is.

OptimizationBehavioral protocol

Seasonal Affective Disorder (SAD) · Circadian Mood Disruption

Recurrent winter-pattern depression tied to a delayed circadian clock, not the same thing as the winter blues.

Circadian-Linked Mood DisorderNo drug approved specifically for SAD; light boxes are unregulated wellness devices, not FDA-cleared for SAD. Bupropion XL is FDA-approved for SAD prevention.

Evening Light Exposure & Devices

The wavelength gets the blame, but brightness, and what you do on the screen, matter more.

DisruptionConsumer products vary

Magnesium, Glycine, Theanine, Apigenin & More

Magnesium, glycine, and theanine have real (modest) data. Most sleep stacks oversell.

OptimizationSupplements (vary)

Sleep Trackers & Wearables · Measurement

These devices measure movement, heart rate, HRV and temperature. They infer sleep stages.

MeasurementGeneral sleep tracking is wellness, un-cleared. Specific features cleared: Apple Watch ECG/AFib (510k) and sleep apnea notification (cleared Sept 2024, US); Samsung sleep apnea (De Novo, 2024, US). Sleep-stage output is not FDA cleared.