  We present a mechanism to endow the polariton gas with attractive
interactions. The scheme relies on an exciton reservoir, which can be formed
even if excitons lie outside of the light-cone. Such an attractive interaction
should open new routes in the physics of quantum fluids, that we illustrate
with a simple but nontrivial application whereby the polariton condensate
enters the self-oscillation regime powered by the attraction from the
reservoir. This results in pulsed emission in the GhZ regime.
