[5] Deflazacort carries the risks common to all corticosteroids, including immune suppression, decreased bone density, steroid induced muscle atrophy, myopathy and endocrine insufficiency.

In clinical trials, the most common side effects (>10% above placebo) were Cushing's-like appearance, weight gain, and increased appetite.

[1] In January 2015, the FDA granted fast track status to Marathon Pharmaceuticals to pursue approval of deflazacort as a potential treatment for Duchenne muscular dystrophy, a rare, "progressive and fatal disease" that affects boys.

[10] Although deflazacort was approved by the FDA for use in treatment of Duchenne muscular dystrophy on February 9, 2017,[11][12] Marathon CEO announced on February 13, 2017, that the launch of deflazacort (Emflaza) would be delayed amidst controversy over the steep price Marathon was asking for the drug in the United States - $89,000 per year, which is "roughly 70 times" more than it would cost overseas.

[16] The U.S. Food and Drug Administration approved deflazacort to treat people age five years and older with Duchenne muscular dystrophy (DMD), a rare genetic disorder that causes progressive muscle deterioration and weakness.