Does Grapefruit Affect Melatonin?

Amount or timing may matter

The short answer

Melatonin is metabolized primarily by CYP1A2 (and partly CYP3A4). Grapefruit inhibition of these enzymes can increase melatonin blood levels and prolong sedation.

How to arrange timing

Avoid grapefruit within 4 hours of melatonin. Excessive sedation and next-day drowsiness may occur.

Reference

Reference noted for this food and supplement combination: Hartter et al., Clin Pharmacol Ther 2003

Important context

The effect can also change with food amount, supplement dose, product formulation, health conditions, and medication use. Ask a doctor or pharmacist first if you take medication, are pregnant or breastfeeding, or have a chronic condition.