The effects of quadratic drag and vertical throughflow on the onset of double diffusive convection in a non-Newtonian fluid saturated horizontal porous layer are investigated. A modified Forchheimer-extended Darcy model which takes inertia into account and viscoelastic effects is employed to describe the flow in a porous medium. The boundaries are considered to be impermeable but perfect conductors of heat and solute concentration. Conditions for the occurrence of stationary and oscillatory convection are obtained analytically using the Galerkin technique. In contrast to the single component system, it is found that a small amount of throughflow in either of its direction destabilizes the system.