Hi & Welcome. Used in the treatment of relapsing forms of multiple sclerosis (MS), Tecfidera (Dimethyl fumarate) is known to cause flushing of the skin, rash, itching and gastrointestinal problems (such as diarrhoea, nausea, and pain in the abdominal area). These side effects tend to start early during treatment, usually in the first month, and may continue intermittently throughout treatment and are usually well tolerated. You can consult your treating doctor for further evaluation to either adjust the dose of Tecfidera or to prescribed alternate effective but safer medications like Beta interferons or Fingolimod or Alemtuzumab. Hope this answers your query. Best regards.