The overall safety profile was similar to that demonstrated in previous studies ; tapentadol ER was associated with a lower incidence of gastrointestinal treatment-emergent adverse events than morphine SR [ 38.0 % ( 19/50 ) vs. 54.0 % ( 27/50 ) ] , including constipation [ 12.0 % ( 6/50 ) vs. 20.0 % ( 10/50 ) ] and vomiting [ 6.0 % ( 3/50 ) vs. 26.0 % ( 13/50 ) ] .