Dear Editor, In their network meta-analyses (NMAs) of treatments for ulcerative colitis (UC), Singh et al1 did not take into account a complication associated with studies that re-randomized patients for the maintenance phase: differential carryover effects from induction can bias the results. In those studies, patients who responded to induction were re-randomized to maintenance treatments that included placebo. If, however, carryover effects from induction differ substantially among active treatments, the effects of those treatments, relative to placebo, are not comparable.