  The Coleman formula for vacuum decay and bubble nucleation has been used to
estimate the tunneling rate in models of axion monodromy in recent literature.
However, several of Coleman's original assumptions do not hold for such models.
Here we derive a new estimate with this in mind using a similar Euclidean
procedure. We find that there are significant regions of parameter space for
which the tunneling rate in axion monodromy is not well approximated by the
Coleman formula. However, there is also a regime relevant to large field
inflation in which both estimates parametrically agree. We also briefly comment
on the applications of our results to the relaxion scenario.
