I'm thinking that msm may be the reason behind my headaches too! I get headaches pretty frequently anyway, not migraines, but annoying and painful nonetheless, but the day after I started taking msm, I had the worst headache EVE! And I had no medicine with me. I again had a very painful headache the next day and the msm was the only thing that had changed. However, after the first week, everything seems to be back to normal. Maybe it's something you just have to get used too.