🛏 Melatonin Timing & Circadian Phase Shift Simulator

Core Body Temperature Minimum Sets the Clock Reference

Every phase-shift calculation starts from one anchor: Tmin.

• ~4–5 AM: Typical Tmin time (roughly 2h before habitual wake)
• Later: Tmin drift, DSPS (delayed relative to clock time)
• Unchanged: Tmin drift, jet lag (stays on home-timezone clock)
• Endogenous: Marker rhythm (set by the SCN pacemaker)

Why Tmin, not clock time

Clock hours mean nothing without knowing where Tmin sits.

Estimating Tmin without a lab

Approximated as about two hours before habitual wake time.

All dosing timing in this simulator is relative to Tmin, not wall-clock time.

Tmin moves with the disorder

DSPS pushes Tmin later; jet lag leaves it on the old zone.

The Melatonin Phase Response Curve

Melatonin's effect flips sign depending on when it is taken.

• ~1–2 h: Max shift per dose (typical low-dose magnitude)
• Before Tmin: Advance zone (afternoon–evening window)
• After Tmin: Delay zone (early morning window)
• Midday: Dead zone (minimal shifting effect)

A curve, not a single rule

The PRC maps dose timing to shift direction and size.

Opposite of the light PRC

Melatonin's advance zone sits where light's delay zone sits.

Melatonin advances before Tmin and delays after Tmin — inverse of light.

Magnitude fades near the edges

Shift size shrinks the farther a dose sits from Tmin.

Evening Dosing Before Tmin Advances the Clock

A dose several hours before Tmin pulls sleep timing earlier.

• −5 to −3 h: Best window (before Tmin)
• 0.5 mg: Typical dose (low dose favored for timing)
• Earlier sleep: Result (bedtime and wake shift earlier)
• DSPS: Use case (delayed sleep phase syndrome)

Evening timing, not bedtime

The dose targets hours before Tmin, not lights-out itself.

Low dose beats high dose here

Small doses shift phase better than sedating high doses.

A low evening dose several hours before Tmin produces the largest advance.

Cumulative daily advances

Repeated evening doses walk Tmin earlier day by day.

Morning Dosing After Tmin Delays the Clock

A dose shortly after Tmin pushes sleep timing later.

• +3 to +5 h: Best window (after Tmin)
• Later sleep: Result (bedtime and wake shift later)
• Westward travel: Use case (or advanced sleep phase)
• Daytime sedation: Risk (dosing after normal wake time)

Morning zone is narrower

The delay window is real but smaller than the advance zone.

Rarely the therapeutic goal

Most travelers and DSPS patients want advances, not delays.

Dosing after Tmin is useful mainly for westward travel or advanced sleep phase.

Watch for daytime drowsiness

Post-Tmin dosing can overlap with normal wake hours.

Matching the Goal to the Correct Dosing Window

Eastward jet lag and delayed sleep phase both call for advances.

• Advance: Eastward jet lag (evening dose, before Tmin)
• Delay: Westward jet lag (morning dose, after Tmin)
• Advance: Delayed sleep phase (evening dose, before Tmin)
• Delay: Advanced sleep phase (morning dose, after Tmin)

Match direction to the goal first

Wrong-side dosing wastes days or shifts the clock backward.

Eastward travel needs advances

Flying east demands an earlier clock, so dose before Tmin.

Both eastward jet lag and DSPS are corrected the same way: dose before Tmin.

Full adjustment takes days

Daily small shifts accumulate toward the total needed correction.