The impact of hydrogen in ZnO is revealed by combining reaction dynamics calculations with temperature dependent Hall (TDH), photoluminescence, and secondary ion mass spectrometry measurements performed on H, 2H, and He implanted ZnO. H and 2H box profiles with a concentration ranging from ∼3×1017 cm−3 to ∼1019 cm−3 and He to produce as much as damage as in the [H] ∼3×1017 cm−3 case were implanted in the samples. The formation of Li lean regions has been observed for [2H] <1019 cm−3 after annealing at 400 ∘C. This is attributed to Lii presence consequent to the diffusion of Zni created during the H/2H implantation process. Results extracted from the TDH measurements performed prior to the annealing at 400 ∘C evidence that Lii contributes to an increase in carrier concentration up to ∼1017 cm−3 by providing a donor level with an activation energy of ∼40 meV and thus is very close to the value of ∼47 meV expected for H in the oxygen site. The reaction dynamics analysis evidences that the amount of Lii introduced is decreasing at higher H implantation doses as a result of increasing VZn and H-VZn retrapping, reactions in which Lii is competing with H. Overall, due to Lii formation as well as the presence of Al the maximum percentage of the implanted H or 2H acting as a donor in the investigated range is found to be ≲ 2%, which is considerably lower than previously reported.