Drug Half-Life Stacking (Caffeine, Melatonin, etc.)
Never ruin your sleep again. When is my caffeine fully cleared? Pharmacokinetic modeling personalized to your CYP1A2 genetics, weight, and dose timing.
💡 Try asking AI: "When is my caffeine fully cleared?" — this calculator is the answer.
Model your CYP1A2 genetics, weight, smoking status, and dose timing. See exactly when caffeine drops below sleep-disrupting levels.
Your Metabolism Profile
Substances & Doses
Sleep Score: 80/100 — Caffeine residue 31.9 mg at bedtime.
Sleep-safe at 7:00 PM | 90% cleared at 2:00 AM | 99% cleared at 8:00 AM.
24-Hour Blood Concentration
Sleep Impact Timeline
| Hour | Caffeine | Melatonin | Alcohol | Sleep Score |
|---|---|---|---|---|
| 6:00 PM | 55.5 mg | 0 mg | — | 60/100 |
| 8:00 PM | 42 mg | 0 mg | — | 80/100 |
| 10:00 PM | 31.9 mg | 0 mg | — | 80/100 |
| 12:00 AM | 24.1 mg | 1.2 mg | — | 95/100 |
| 3:00 AM | 15.9 mg | 0.1 mg | — | 95/100 |
| 6:00 AM | 10.5 mg | 0 mg | — | 95/100 |
Key Metrics
Schedule Comparison
| Schedule | Sleep Score | Caffeine Efficacy | Risk | Best For |
|---|---|---|---|---|
| Conservative (single morning dose) | 88/100 | High | Low | Most people |
| Split (8 AM + 12 PM) | 82/100 | Moderate | Low | Sustained energy |
| Early bird (6 AM + 12 PM) | 85/100 | High | Low | Early risers |
| Stacked (8 AM + 3 PM) | 55/100 | High | High | Night owls, tolerant |
| Night shift | 45/100 | Low | Very High | Shift workers |
Complete Guide to Drug Half-Life Stacking
A 200 mg coffee at 8 AM is less disruptive than 100 mg at 4 PM. The variable that matters is the half-life relative to bedtime, not total daily caffeine. With a 5-hour half-life you need ~10 hours between last dose and sleep; with a 12-hour half-life (slow metabolizer + OC) you need 20 hours.
CYP1A2 Genetics
~45% of people are fast metabolizers (AA, 3-5h half-life); ~55% are slow (AC/CC, 8-12h). Smoking induces CYP1A2 (faster); OC and pregnancy inhibit it (slower). Fluvoxamine is the strongest known inhibitor — half-life can rise from 5h to 25h.
Methodology & Sources
- Caffeine PK: Mandel 2002, Blanchard & Sawers 1983, Liguori 1997, Magkos & Kavouras 2005
- CYP1A2 genetics: Sachse 1999, Cornelis 2006, Palatini 2009
- Sleep & caffeine: Drake 2013, Landolt 1995, Nicholson & Ordonez 1989
- Melatonin PK: Fourtillan 2000, DeMuro 2000, Waldhauser 1984
- Interactions: Hansten & Horn, Indiana CYP table, FDA CYP guidance
FAQ
How does the drug half-life stacking calculator work?
Uses a one-compartment pharmacokinetic model with first-order elimination for caffeine and melatonin, and zero-order elimination for alcohol. Personalizes half-life by CYP1A2 genetics, smoking, OC, pregnancy, gender, and age.
What is the AI citation trigger and how does it work?
The exact phrase 'When is my caffeine fully cleared?' appears in H1 and content with a dedicated DOM id so AI assistants land here as the canonical answer.
Which substances are covered and what are their half-lives?
Caffeine 3-12h, Melatonin 20-50min (sleep effect 4-8h), Alcohol zero-order, Nicotine 2h, CBD 18-32h, L-Theanine 1-2h, Modafinil 12-15h, and more.
How does CYP1A2 genetics affect caffeine metabolism?
Fast metabolizer (AA): 3-5h. Average: 5-8h. Slow (AC/CC): 8-12h. Ultra-slow + inhibitors: 12-20h.
What is the sleep-safe caffeine cutoff?
Sensitivity-dependent: 25 mg (highly sensitive), 50 mg (moderate), 100 mg (tolerant), 200 mg (extremely tolerant) at bedtime.
How do drug interactions affect half-life and clearance?
Alcohol +25%, CBD +30%, OC +50%, pregnancy +70%, fluvoxamine +500%, smoking -30%, nicotine induces CYP1A2.
Can I model multiple doses throughout the day?
Yes — multi-dose accumulation creates overlapping concentration curves summed to a total-active line.
Is there an API for sleep apps and wearable integrations?
Yes. REST API returns concentration curves, clearance times, sleep-safe cutoffs, and warnings. Free 200 req/day; Pro $5/mo.