  Z' gauge bosons arise in many particle physics models as mediators between
the dark and visible sectors. We exploit dark matter complementarity and derive
stringent and robust collider, direct and indirect constraints, as well as
limits from the muon magnetic moment. We rule out almost the entire region of
the parameter space that yields the right dark matter thermal relic abundance,
using a generic parametrization of the Z'-fermion couplings normalized to the
Standard Model Z-fermion couplings for dark matter masses in the 8 GeV-5 TeV
range. We conclude that mediators lighter than 2.1 TeV are excluded regardless
of the DM mass, and that depending on the Z'-fermion coupling strength much
heavier masses are needed to reproduce the DM thermal relic abundance while
avoiding existing limits.
