Do not use if migraine prone.
Migraines and headaches plagued my life until I removed gluten from my diet. After more than 10 years free from any headaches or migraines I had a migraine on the third day after starting to use this product. It seems the MSM was most likely the problem as it has a noted side effect of causing migraines, especially in those who are migraine prone. Taking a glucosamine product without the MSM has not caused any problems for myself. The MSM component of this product seems to be a high risk substance for any one who has ever had a migraine problem as noted elsewhere on the internet.