When to Stop

• Caffeine toxicity — symptoms (severe anxiety, vomiting, arrhythmia, seizure) at single doses >500-1000mg in caffeine-naive; >1500-3000mg lethal range. Powdered caffeine has caused fatal overdoses from kitchen-scale errors. Rule: only dose pre-portioned tablets (100-200mg) — never powder unless using a milligram-precision scale.
• Atrial fibrillation / arrhythmia — rare; mostly in pre-existing arrhythmia or very high doses.
• Caffeine-induced anxiety disorder, sleep disorder — DSM-5 listed; mostly in heavy users (>500-1000mg/day) or anxiety-prone subgroups.
• Hypertensive interaction with stimulant drugs (modafinil, amphetamines) — additive cardiovascular load.
• Pregnancy — not relevant for users in this archetype; mention only because it's the most common medical-warning context.
• Week 1-2: GI tolerance window — start with 50-100mg + food, scale up only if no GI distress.
• Week 1-4: tolerance development risk — if dosing daily, expect responsiveness drop by week 2; skip days proactively to prevent.
• First 6 months of regular use: sleep architecture audit — Oura ring or sleep tracker to verify caffeine timing isn't degrading deep/REM sleep. Don't trust subjective "I sleep fine" — the 2025 athlete data shows subjective-objective disconnect is the rule, not the exception.