  We study the effects of dissipation on a disordered quantum phase transition
with O$(N)$ order parameter symmetry by applying a strong-disorder
renormalization group to the Landau-Ginzburg-Wilson field theory of the
problem. We find that Ohmic dissipation results in a non-perturbative
infinite-randomness critical point with unconventional activated dynamical
scaling while superohmic damping leads to conventional behavior. We discuss
applications to the superconductor-metal transition in nanowires and to Hertz'
theory of the itinerant antiferromagnetic transition.
