Using a three-dimensional chemistry-climate model of the troposphere and stratosphere, we find that hydrogen sulfide alone is unlikely to directly affect stratospheric ozone, even for hydrogen sulfide emission rates as large as 5000 Tg(S) per year. However, we also find that large quantities of hydrogen sulfide create a significant decrease in tropospheric hydroxyl radical, leading to a commensurate increase in atmospheric methane. Therefore a large methane flux (possibly from methane clathrate destabilization, Siberian traps or hydrothermal vent complexes) combined with a large hydrogen sulfide oceanic flux is much more likely to lead to an ozone collapse than methane or hydrogen sulfide alone with implications to the Permian-Triassic boundary extinction 250 million years ago.