How long does riboflavin 400 mg take to cut migraines, and can I safely stack it with magnesium?

Short answer: plan on a full 3-month trial. In the main randomized trial (Schoenen 1998, n=55), riboflavin 400 mg once daily gave a 50%+ reduction in attack frequency in 59% of patients versus 15% on placebo. Benefit was clearer at month 3 than at month 1. Take it with food for better absorption. Expect bright yellow urine, which is harmless. Magnesium is a reasonable add-on, and many people take both. Use 200-400 mg of elemental magnesium in the evening and track the elemental amount, not the compound weight. Magnesium glycinate is only about 14% elemental, so 400 mg elemental is roughly 2,800 mg of powder. Keep a headache diary with attack days, triptan days and dose changes. Judge the result after 12 weeks. Check with your prescriber first if you have reduced kidney function.