Cohesion can dramatically affect the flow of granular media. In this Letter, thanks to a cohesion-controlled granular material, we propose to investigate experimentally the effect of the cohesion on the discharge from a silo. We use two geometries, a cylindrical silo and a thin rectangular silo, with an adjustable bottom to control the size of the orifice. Similarly to cohesionless granular material, the mass flow rate is mostly controlled by the diameter of the outlet D, however, we observe that the cohesion tends to decrease the flow rate. We show that this effect is controlled by a cohesive length, based on the cohesive yield stress and gravity acceleration, which acts as an effective particle size. This cohesive length is also found to control the onset of flow.