  The detectability of light dark matter in direct detection experiments is
limited by the small kinetic energy of the recoiling targets. Thus, scenarios
where dark matter is boosted to relativistic velocities provide a useful tactic
to constrain sub-GeV dark matter particles. Of the possible dark matter
boosting mechanisms, cosmic-ray upscattering is an appealing paradigm as it
doesn't require any additional assumptions beyond dark matter coupling to
nucleons or electrons. However, detectable signals are obtained only with
relatively large cross sections which, in turn, can only be realized with large
couplings, light mediators or composite dark matter. In this work we consider a
general set of light mediators that couple dark matter to hadrons. Using data
from Borexino, XENON1T, LZ and Super-K, we show that existing constraints on
such mediators preclude appreciable cosmic-ray dark matter upscattering. This
finding highlights the limited applicability of cosmic-ray upscattering
constraints and suggests they only be used in model-dependent studies.
