Hyperbaric oxygenation was used in the treatment of 340 patients with narcomania, toxicomania, and alcoholism in the post-intoxication and abstinence periods; 223 of these were alcoholics, 68 toxicomaniacs, and 49 opium narcomaniacs. A group of 185 patients administered drug therapy alone were controls. Exposure to hyperbaric oxygenation had a favorable effect on the patient's status during sessions and persisted for some time after them. Patients with different premorbid symptoms and initial status experienced tranquilizing or bioenergizing effects of hyperbaric oxygen. A comparative clinical and psychopathological examination of patients in both groups showed accelerated reduction of psychoneurological and somatovegetative disorders, this bringing about an approximately twofold decrease of treatment duration and preventing the development of complications. The parameters of central hemodynamics normalized and myocardial status improved, which helped prevent the development of cardiovascular decompensation. Such a favorable time course of events appears to be due to the antihypoxic detoxifying and bioenergetic effects of hyperbaric oxygen.