  Early decoupling of thermally produced dark matter particles due to feeble
interactions with the surrounding plasma typically results in their excessive
abundance. In this work we propose a simple mechanism for dark matter
depopulation. It relies on a specific cosmological evolution under which dark
matter particles become temporarily unstable and hence decay away reducing the
overall abundance. The instability phase may be followed by an incomplete
regeneration phase until the final abundance is established. We explicitly
demonstrate this mechanism within a simple toy model of fermionic dark matter
and discuss how it can be implemented in theoretically well motivated theories,
such as the minimal supersymmetric standard model (MSSM) and for fermionic dark
matter in the scotogenic model.
