  Dark Matter (DM) may be a thermal relic that annihilates into heavier states
in the early Universe. This Forbidden DM framework accommodates a wide range of
DM masses from keV to weak scales. An exponential hierarchy between the DM mass
and the weak scale follows from the exponential suppression of the thermally
averaged cross section. Stringent constraints from the cosmic microwave
background are evaded because annihilations turn off at late times. We provide
an example where DM annihilates into dark photons, which is testable through
large DM self-interactions and direct detection.
