How to take Dimethyl Fumarate. Take this medication by mouth with or without food as directed by your doctor, usually twice daily. Your doctor should usually direct you to start this medication at a low dose for the first 7 days of treatment and to increase your dose after 7 days. Follow your doctor’s instructions carefully. If flushing occurs, taking this medication with food may reduce this side effect. Taking a plain (non-enteric coated) aspirin 30 minutes before taking this medication may also help prevent flushing.