Abstract: The invention relates to a gas mixture that contains nitrous oxide (N2O) for use as a breathable drug for the treatment of chronic pain in a mammal, in particular a pain from neuropathic, iatrogenic, dysfunctional or inflammatory origin, in particular in humans. The proportion of N2O ranges from 15 to 45 vol. %. The gas mixture is administered for a sufficient duration for obtaining a delayed pain hypersensitivity reduction that can be observed at least 6 hours after the end of the inhalation of the gas mixture by said mammal. The pain hypersensitivity is selected from allodynias and hyperalgesias.