From the contributors at Wikipedia:
The oxygen cocktail was developed in the 1960s by the Russian academician N. N. Sirotinin. While researching the respiratory function of the stomach and the possibility of filling the body with oxygen through the digestive tract, Soviet doctors put probes into the patients’ stomachs, through which the body could be filled with up to 2 liters of oxygen. Although the condition of the patients improved considerably, this method had to be abandoned because of discomfort caused by the probes. In an alternative treatment, a foam-forming liquid was filled with oxygen and transferred to the patient’s mouth via a tube. Later, researches suggested adding the oxygen foam into food or drink. Such oxygen-enriched drinks received the name “oxygen cocktail” and were produced in sanatoriums and clinics. Since the 1970s, the method of making such drinks has undergone almost no changes, but the foam-forming ingredients and the ways of filling the cocktails with oxygen have been improved.
Juices (grape, cherry, raspberry, etc.), syrups, water, milk and fruit-drinks are often used as the base of the cocktail. Oily and sparkling liquids result in poor homogeneity of the foam. The base liquid might contain extracts of plants and herbs such as hawthorn, strawflower, and >rose hip, which themselves are used in the clinical practices. An essential element of the oxygen cocktail is the foaming agent, such as gelatin egg white or liquorice. Initially, oxygen cocktails were made with egg white. However clinical trials proved that this ingredient resulted in allergenicity and unpleasant taste and could promote infectious diseases; thus it was replaced by liquorice, which is a foaming agent, tonic and sedative.