Onfi (clobazam) is a benzodiazepine that is prescribed to treat seizures caused by Lennox-Gastaut syndrome. On Dec. 3, 2013, the Food and Drug Administration approved the addition of Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) to the adverse effects listed on the drug’s label. SJS and its more serious counterpart TEN are severe skin conditions where layers of the skin are pulled apart by the death of their respective cells.