1000–2000 IU daily with a fatty meal (breakfast or lunch works well). If you're deficient or live in a southern state, 4000 IU daily is safe and more effective. Ideally, get your levels tested first — aim for 75–100 nmol/L.

500–1000 mg daily split into 2–3 doses throughout the day (e.g., 500 mg with breakfast and 500 mg with dinner). If you feel a cold coming on, increase to 1000 mg daily for 1–2 weeks. Avoid exceeding 2000 mg daily unless under medical guidance.

15–30 mg daily during cold/flu season as a preventative, or 15–30 mg at the first sign of symptoms for 1–2 weeks. Lozenges are particularly effective (75 mg+ per lozenge) if you can tolerate them — dissolve slowly in your mouth rather than swallowing whole.

500–1000 mg daily, taken with vitamin C and a meal for best absorption. If combining with zinc, take them together — quercetin enhances zinc's cellular uptake. Use for 2–4 weeks during cold season or when you feel vulnerable.