The Safety Profile of HBOT: What a Meta-Analysis of Adverse Effects Shows
A meta-analysis of 24 trials finds HBOT's most common adverse effect is ear barotrauma, with serious events rare. Why supervised operation and screening still matter.
- A meta-analysis of 24 randomised trials (1,497 participants) found HBOT's most common adverse effect is middle-ear barotrauma, with serious events rare.
- Adverse effects were more common with HBOT than control (about 30 percent versus 10 percent), but the great majority were mild and manageable.
- Risk scaled with exposure: courses over 10 sessions and pressures above 2.0 ATA were linked to more adverse effects than shorter, lower-pressure courses.
The evidence base
A systematic review and meta-analysis pooled 24 randomised controlled trials with 1,497 participants to characterise the adverse effects of hyperbaric oxygen therapy, drawing on trials published in the decade to 2022. The headline is a matter of proportion: adverse effects were more common in HBOT groups than in control groups (about 30 percent versus about 10 percent), but the most frequent events were minor and manageable rather than dangerous. Put differently, the comparison is not treatment-with-risk versus no-risk, but a modest, mostly mild increase in side effects that has to be set against any potential benefit.
Reading a safety profile well means holding two ideas at once - that side effects are more common with treatment, and that the great majority of them are mild. The trials pooled here spanned a range of conditions and protocols, so the overall figures describe hyperbaric oxygen broadly rather than any single indication.
The most common problem: the ears
The single most frequently reported problem was ear discomfort, tied to middle-ear barotrauma, which formed by far the largest category of events. Barotrauma occurs when pressure changes are not equalised across the eardrum during compression or decompression, and it is usually mild and self-limiting.
It is also the most predictable reason a session is uncomfortable, which is why controlled compression rates and equalisation technique matter, and why trained operators coach patients through them. In practice, a slower compression and coaching patients to equalise are the usual ways clinics reduce this risk.
Dose matters: pressure and number of sessions
The analysis found that risk was not fixed but scaled with exposure. When a course ran longer than 10 sessions, adverse effects were more common than in control groups; shorter courses of 10 sessions or fewer looked comparatively benign. Similarly, chamber pressures above 2.0 ATA were associated with a higher incidence of adverse effects.
In plain terms, more pressure and more sessions carry more to monitor. That is an argument for protocols matched to the situation, not for maximal exposure as a default, and it helps explain why side-effect rates differ so much between studies: a short, low-pressure course and a long, high-pressure one are simply not the same exposure.
Rare but real, and why supervision matters
Beyond the ears, hyperbaric oxygen carries recognised but less common risks, including oxygen toxicity affecting the lungs or central nervous system, and there are medical contraindications that pre-treatment screening is meant to catch. Serious events are rare, but 'rare' is not 'never', which is the reason trained supervision, proper screening and a well-maintained chamber are non-negotiable. Screening exists to identify the people for whom the balance of risk and benefit is unfavourable before the first session, not after. If you are comparing the settings in which HBOT is delivered, our chamber-type overview at HBOT chambers outlines the main categories.
A favourable safety profile is not the same as a green light for everyone. Whether HBOT is suitable, at what pressure and for how many sessions, is a judgement for a physician who can screen for contraindications first.
Frequently asked questions
+What is the most common side effect of HBOT?
Ear discomfort tied to middle-ear barotrauma is by far the most frequently reported problem in this meta-analysis. Barotrauma occurs when pressure changes are not equalised across the eardrum during compression or decompression, and it is usually mild and self-limiting. It is also the most predictable reason a session is uncomfortable, which is why clinics use controlled, slower compression rates and coach patients through equalisation technique.
+How safe is HBOT overall?
The meta-analysis found adverse effects were more common with HBOT than control (about 30 percent versus 10 percent), but the great majority were minor and manageable, and serious events were rare. Rare, however, is not never: recognised risks include oxygen toxicity affecting the lungs or CNS, plus contraindications screening is meant to catch. Whether HBOT is suitable, and at what dose, is a judgement for a physician who screens first.
+Does the number of sessions or pressure change the risk?
Yes. The analysis found risk scaled with exposure. Courses longer than 10 sessions saw more adverse effects than control groups, while shorter courses of 10 or fewer looked comparatively benign, and pressures above 2.0 ATA carried a higher incidence. In plain terms, more pressure and more sessions mean more to monitor - an argument for protocols matched to the situation, decided with a supervising physician.