Does Grapefruit Affect Modafinil?

Amount or timing may matter

The short answer

Modafinil is a CYP3A4 substrate. Grapefruit may increase modafinil blood levels, causing excessive stimulation, insomnia, or cardiovascular effects.

How to arrange timing

Avoid grapefruit within 4 hours of taking modafinil.

Reference

Reference noted for this food and supplement combination: Robertson & Hellriegel, Clin Pharmacokinet 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.