Hi . We are not medical experts, so keep that in mind as I respond. As far as I know, Tecfidera works by reducing the inflammatory response in your body. It takes six month to two years to become fully effective. So it is unlikely it would have had an impact on you in five days. The relapse might have been a coincidence. Did your doctor offer you anything to help with the relapse, like a round of steroids? What has your neurologist said about the timing of the relapse in relation to your medication? I hope you begin to recover soon and that you make a decision about treatment that gives you confidence. Best of all wishes. - Lori (Team Member)