Ozone therapy carries a range of side effects, from common and mild reactions like fatigue and nausea to rare but serious complications including stroke and severe allergic reactions. The most frequent side effect is temporary tiredness, reported by 20 to 30 percent of patients after their first several sessions. It’s also worth noting that the FDA considers ozone “a toxic gas with no known useful medical application,” meaning this treatment exists largely outside mainstream medical regulation in the United States.
Common Mild Side Effects
The most well-documented side effects come from autohemotherapy, where blood is drawn, mixed with ozone, and reinfused. In clinical observations, 20 to 30 percent of patients reported feeling tired for about a day after each of the first four or five treatments. This fatigue typically fades as sessions continue.
Nausea, stomach bloating, and a metallic taste in the mouth have been reported by 10 to 15 percent of patients, more often in women. Some patients, again mostly women, also experienced a tingling sensation in the lips and tongue toward the end of a blood reinfusion. On the other end of the spectrum, about 50 percent of patients reported actually feeling better after treatment, and another 10 to 20 percent noticed no symptoms at all.
Some people experience what’s called a Herxheimer reaction: flu-like symptoms that can develop as the body responds to the inflammatory and antimicrobial effects of ozone. These symptoms are generally short-lived but can be uncomfortable enough to catch you off guard if you’re not expecting them.
Allergic and Skin Reactions
A small number of patients have developed more significant allergic responses. In one clinical series, four women developed a sudden, widespread red skin rash with itching, nausea, hot flushes, and a drop in blood pressure at the end of a blood reinfusion. One of those patients had a prior history of anaphylactic shock from a wasp sting, suggesting that people with existing allergic tendencies may be at higher risk. These reactions appeared after 4 to 12 treatment sessions, not necessarily on the first visit, which means you can’t always predict them from an initial treatment.
Skin irritation has also been reported following topical ozone application, where the gas is applied directly to the skin surface.
Serious Complications
The most dangerous risk of ozone therapy is gas embolism, where ozone or oxygen bubbles accidentally enter the bloodstream and block blood vessels. In one documented case, a 58-year-old woman arrived at an emergency department with sudden speech difficulty and weakness in her limbs after an ozone session. Imaging revealed that gas bubbles had traveled through her arteries and caused damage to both sides of her brain, resulting in a multifocal stroke.
Gas embolism can happen when ozone enters the arterial circulation directly, or when bubbles in the venous system cross into arteries through small defects in the heart or lungs (a pathway called paradoxical embolism). People with undiagnosed heart defects may be at elevated risk without knowing it. Symptoms can include sudden confusion, weakness on one side of the body, seizures, or loss of consciousness.
Ozone injections, particularly those used for spinal conditions like lumbar disc herniation, carry their own set of serious risks. Documented complications include bleeding in the eye, nerve root injury, stroke affecting the back of the brain, spinal infections, abscesses, and in rare cases, fatal bloodstream infections. When ozone is injected into wounds such as diabetic foot ulcers, there is also concern that it can push surface-level infections deeper into tissue.
Respiratory Risks From Inhalation
Ozone should never be inhaled directly. Even at low concentrations, it irritates the airways. At higher levels (around 9 parts per million), it can cause pulmonary edema, a dangerous buildup of fluid in the lungs. For context, the EPA’s outdoor air quality threshold for ozone is 0.070 ppm, more than 100 times lower than the level linked to pulmonary edema. Respiratory irritation can also occur simply from being near an ozone generator during treatment, even when the therapy itself targets a different part of the body.
Who Should Avoid Ozone Therapy
People with G6PD deficiency, an inherited enzyme condition affecting more than 400 million people worldwide, face a specific and serious risk. G6PD-deficient red blood cells are vulnerable to oxidative stress, which is exactly what ozone creates. Exposure can trigger hemolysis, the rapid destruction of red blood cells, which can become life-threatening. G6PD deficiency is most common in people of African, Mediterranean, and Southeast Asian descent, and many carriers don’t know they have it.
Pregnant women and people with uncontrolled hyperthyroidism are also generally advised against ozone therapy. Anyone with a history of severe allergic reactions or anaphylaxis should approach treatment with particular caution given the allergic responses observed in clinical settings.
The FDA’s Position
The FDA’s stance is unambiguous: ozone is classified as a toxic gas with no proven medical use. Federal regulations state that any ozone-generating device used for medical treatment is considered adulterated or misbranded if applied to “any medical condition for which there is no proof of safety and effectiveness.” This means ozone therapy devices cannot be legally marketed for medical purposes in the U.S., though practitioners in some states continue to offer treatments under various regulatory gray areas.
This regulatory gap matters because it means the equipment, dosing protocols, and practitioner training you encounter can vary enormously from one clinic to the next. Many of the side effects documented in clinical observations, particularly the nausea, metallic taste, and allergic reactions from autohemotherapy, were later attributed to specific equipment choices (PVC bags that leached chemical additives into the blood). When clinics switched to glass bottles and more precise dosing, those particular side effects reportedly disappeared. The quality of equipment and the experience of the person administering treatment directly affect your risk profile, and without standardized regulation, there is no reliable way to verify either before your appointment.