Ergocalciferol
"Was prescribed 50000 iu of Drisdol once a week for 12 weeks. I was reluctant to take it since OTC Vitamin D3 triggers migraines. My doctor  assured me that, since Drisdol was Vitamin D2 NOT D3  it wouldn't cause headaches. Boy was he WRONG. With 24 hours after taking the first capsule I had a severe migraine that none of my usual meds even made a dent it.  I ended suffering up in bed for three days. Oh, did I mention the horrible knee pain that came along with the migraine?? I guess I was lucky that I had to stay in bed since my legs hurt too bad to walk. Needless to say,I  stopped the Drisdol. I'm sure my doctor won't be happy with my decision but if he had the reaction to Drisdol that I had I'm sure he would stop taking it too."