Oxygen therapy, or hyperoxygenation therapy, is a quack medical treatment claimed by its proponents to treat several diseases including AIDS, cancer, and Lyme disease. The term is a catch-all for several different treatments, which include: ingesting or injecting hydrogen peroxide, ozone therapy of various kinds, drinking so-called "oxygenated water" products, and the inhalation of pure oxygen. In the case of ozone therapy, the theory seems to be that, because O2 is generally necessary for human life, O3 must be some kind of SUPER OXYGEN that is even better for you. Much like hydrogen peroxide (H2O2) is more refreshing than water (H2O).
Oxygen therapy is completely ineffective and potentially dangerous.
Oxygen therapy is based on the false notion that cancer cells and viruses cannot survive in a high-oxygen environment. This may stem from the fact that many tumors are hypoxic (because their rapid growth rate means that blood vessels can't catch up to supply them with sufficient oxygen) but it certainly doesn't mean that an increase in oxygen will kill them - quite the opposite, in fact - and that a low-oxygen environment encourages infectious diseases.
Not only is the theory unsound, but double blind studies of ozone use in AIDS treatment has shown it is ineffective at best. Worse, it was shown to cause greater damage in mice lacking T cells than to regular mice, indicating that those with AIDS (and hence lacking T cells) are at a greater risk for lung injury from ozone. Laboratory studies have also found that high oxygen levels encourage, rather than hinder, the growth of new cancer cells. Anaerobic bacteria may not like oxygen, but everything that has mitochondria has them for the specific purpose of using the energy in oxygen. Thus it stands to reason that oxygen therapy cannot work as a specific cure for cancerous or diseased cells. This isn't to be confused with studies that show aerobic exercise can improve the health and well-being of patients, and diminishing the effect of symptoms.
Autohemotherapy is drawing blood from the patient and bubbling ozone through it, then reinjecting it into the patient. This is potentially dangerous or deadly. 
 Hydrogen peroxide
Some quacks recommend ingestion or injection of hydrogen peroxide, which can be potentially dangerous or deadly. Hydrogen peroxide is only useful when used externally to disinfect wounds. Taking it internally or through injection or enemas can lead to any number of dangerous effects such as gas bubbles forming in the liver, destruction of red blood cells, and kidney failure. It has led to at least one death. It is to be noted that a sufficiently strong solution of hydrogen peroxide can bleach skin semi-permanently (i.e. until the bleached skin sloughs off), which was a fact well known to rocket scientists in the United States during the Cold War; see, H2O2 is quite unstable, and a rather fierce oxidizer, so it's been used quite a bit in rocket propellant research. Among other things, it's been used to fuel jetpacks by blasting a spray of the stuff through a grid of palladium or platinum, both of which have strong catalyzing effects that cause the molecule to break down in catastrophic fashion. In other words, we routinely use rocket fuel as a disinfectant, and it works by exactly the same process by which it powers jet packs; needless to say, why anyone considers that something like that could be good for you when taken internally is a mystery for the ages.
 Oxygenated water
Some other forms of oxygen therapy are not potentially dangerous, but merely worthless wastes of time and money. Drinking so-called "oxygenated water" is a useless quack patent medicine, although there are some claims that it may taste a bit better. Dissolving additional oxygen into water is only of benefit to fish, which extract it through gills, or in river water as part of dealing with the Chemical Oxygen Demand of pollution. The maximum dissolved oxygen content for water - even at cool drinking temperature, as gases dissolve better at low temperature - is around 10 mg/L which isn't actually much higher than the natural dissolved concentration which is about 6-7 mg/L. Even at saturation, this works out as about 10 milliliters of oxygen, something you find in about 50 milliliters of normal air - and about a hundredth of the amount exchanged in a single breath. Even if the difference was non-negligible, the human gut - or of any animal, for that matter - cannot absorb oxygen, so it gives no benefit directly and its effect on the water itself is not chemically significant inside the human body. A similar sort of claim was made by Gillian McKeith regarding eating chlorophyll containing leaves to boost oxygen levels - again, patent nonsense as the gut doesn't absorb oxygen and is certainly not a place where you want high concentrations of it. Oxygenated water is sometimes found in health food stores and is claimed to boost sports performance, despite both scientific theory and studies stating otherwise. As it is no more than water, really, it has been described as "snake oil without the oil (and, for that matter, without the snake)".
 Inhaling extra oxygen
Inhalation of oxygen has legitimate medical uses - e.g. the "oxygen tent" - but is useless in treating diseases such as cancer and AIDS. High concentrations of oxygen can damage the body, notably causing blindness.
Inhalation of ozone at high concentrations can lead to respiratory irritation and coma.
- ↑ http://www.ncbi.nlm.nih.gov/pubmed/1685651
- ↑ http://www.ncbi.nlm.nih.gov/pubmed/3494850
- ↑ Cochrane.org - Aerobic exercise interventions for adults living with HIV/AIDS
- ↑ 
- ↑ http://www.quackwatch.com/01QuackeryRelatedTopics/Cancer/oxygen.html
- ↑ A Prescription For Death?
- ↑ EngineeringToolbox.com - Oxygen solubility data
- ↑ Why oxygen dissolved in water is important.
- ↑ Q: Chemically adding more oxygen to bottled water, resulting in consumer benefits.