Poisoning of the surface hydrogen processes during the hydrogen evolution reaction (her) was studied using a Pd membrane cathode where deuterium was supplied from the back side. Three parameters, the apparent current efficiency of H formation, the ease of deuterium permeation, and the extent of isotopic equilibration, were obtained from the isotopic distributions of gaseous hydrogen evolved from the light water electrolysis. These parameters reflect the difficulty of H absorption into the Pd bulk, the ease of the emergence of subsurface hydrogen (D) and the extent of hydrogen surface diffusion/shuffling, respectively. In sulphuric and perchloric acids, all of these were almost unity, which means that any inhibition was not detectable. In phosphoric acid and Li+ added sulphuric acid, the latter two parameters more or less decreased. Organic additives lowered deuterium permeation but had no effect on the extent of isotopic equilibration; these additives suppressed the deuterium emergence processes without disturbing surface hydrogen diffusion. The influences of the metal additives were different, which can be explained by their catalytic activities reported for the corresponding metals and the deposition states on Pd.