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Hyperbaric Oxygen Therapy for Long COVID: What the Trials Show

Does HBOT help long COVID? One sham-controlled trial found benefits; two later placebo trials found none. What the evidence shows and why it is investigational.

Updated September 14, 2026
11 min read
by Hyperbaric.app

This content is for informational purposes only and does not constitute medical advice. Always consult a healthcare professional. Read full disclaimer

Hyperbaric oxygen therapy (HBOT) is an investigational treatment for long COVID, not an accepted one. A 2022 sham-controlled trial from Israel reported better attention, energy, sleep and pain after 40 sessions. Two later placebo-controlled trials, from Sweden and Belgium, found no difference between HBOT and placebo, and a 2024 living systematic review in The BMJ found no compelling evidence that HBOT works for long COVID.

If you are considering it, go in knowing that the evidence is split, that the positive results come mainly from one research centre, and that the best way to try it is inside a clinical trial.

What is long COVID?

The World Health Organization calls it post COVID-19 condition. Symptoms usually start within 3 months of the initial COVID-19 illness and last at least 2 months. WHO estimates that about 6 in every 100 people who have COVID-19 develop it.

Common symptoms include fatigue, breathlessness, muscle or joint pain and poor sleep, along with headaches, difficulty concentrating and changes in taste. More than 200 different symptoms have been reported. WHO also notes that research on treatments is limited and that large studies are lacking. Current care focuses on relieving symptoms and on rehabilitation.

Is HBOT an approved treatment for long COVID?

No. Long COVID is not on the Undersea and Hyperbaric Medical Society (UHMS) list of approved indications, which covers conditions such as decompression sickness, carbon monoxide poisoning, selected problem wounds and delayed radiation injury. It is not on the current European (ECHM) list either, which dates from a 2016 consensus conference. Our guide to accepted HBOT indications compares the UHMS, ECHM and Medicare lists side by side.

That status matters in practice. It means HBOT for long COVID is offered on the basis of early research, not established guidelines.

Why researchers tested HBOT for long COVID

The Israeli team behind the first trial proposed that some long COVID symptoms may come from injury to brain tissue, caused either by the virus directly or indirectly through inflammation and blood-clotting problems. Their hypothesis was that repeated HBOT sessions could improve blood flow in the brain and encourage the brain to rewire itself (neuroplasticity). That is a plausible idea, but a mechanism is not proof of benefit. Only controlled trials can show whether patients actually improve more than they would with a placebo.

What did the clinical trials find?

TrialPatientsHBOT protocolComparisonMain result
Zilberman-Itskovich et al., Israel (2022)7340 sessions, 2 ATA, 100% oxygen, 90 minSham (air at near-normal pressure)Better global cognition, attention, energy, sleep, psychiatric symptoms and pain than sham
HOT-LoCO, Kjellberg et al., Sweden (2025)8010 sessions over 6 weeks, 2.4 bar, 100% oxygen, 90 minPlacebo (air at 1.34-1.2 bar)No difference in physical function at 13 weeks; both groups improved
D'hoore et al., Belgium (2025)10110 sessions; four groups with different oxygen and pressure combinations21% oxygen at normal pressureNo difference between any of the groups in symptoms, function or cognition

The 2022 Israeli sham-controlled trial

The most cited study was run at the Sagol Center for Hyperbaric Medicine and Research at Shamir Medical Center and published in Scientific Reports. It enrolled adults whose cognitive symptoms had lasted more than 3 months after a confirmed infection. Thirty-seven were randomised to HBOT and 36 to sham.

  • HBOT group: 40 daily sessions, five per week over two months, breathing 100% oxygen at 2 ATA for 90 minutes with short air breaks.
  • Sham group: air at 1.03 ATA for 90 minutes, with a brief rise to 1.2 ATA at the start and chamber noise to make the session feel real.

Compared with sham, the HBOT group improved more in global cognitive function, attention and executive function, and in energy, sleep, psychiatric symptoms and pain interference. The effect sizes were moderate. MRI scans showed changes in brain perfusion and microstructure that the authors linked to the clinical gains. Side effects were reported by 35.1% of the HBOT group and 38.9% of the sham group.

The authors themselves noted that the sample was small, that the best number of sessions is not known, and that long-term results were still to come. Two authors disclosed that they work for AVIV Scientific Ltd, and the senior author disclosed that he is a shareholder.

The same centre later published two follow-ups:

  • A sham-controlled study of heart function randomised 60 patients. In a post-hoc analysis of the 29 patients whose global longitudinal strain (a sensitive measure of left ventricular function) was reduced at the start, it improved more after HBOT than after sham.
  • A one-year follow-up of 31 patients who had received HBOT found that improvements in quality of life, sleep, psychiatric symptoms and pain were still present more than a year later. This follow-up included only treated patients, so it cannot show whether the sham group would have improved over the same period.

HOT-LoCO: the Swedish placebo-controlled trial

The HOT-LoCO trial, run at Karolinska University Hospital and published in BMJ Open in 2025, randomised 80 previously healthy adults aged 18 to 60 with long COVID. One group had 10 HBOT sessions over six weeks (100% oxygen at 2.4 bar for 90 minutes). The other breathed medical air at 1.34-1.2 bar.

At 13 weeks both groups had improved, and there was no significant difference between them in the two primary outcomes, physical functioning and role limitations due to physical health. The authors concluded that 10 sessions did not show more short-term benefit than placebo. An exploratory analysis hinted at a possible long-term effect and a difference between women and men, but the authors described these as hypotheses for future research. Adverse events, most often cough and chest discomfort, occurred in 49% of the HBOT group and 44% of the placebo group.

The Belgian four-arm trial

A 2025 trial in Diving and Hyperbaric Medicine randomised 101 long COVID patients to 10 chamber sessions in one of four groups: 100% oxygen at 2.5 ATA, 40% oxygen at 2.5 ATA, 100% oxygen at normal pressure, or ordinary air at normal pressure. There were no significant differences between any of the groups in symptoms, function or cognitive tests. Some patients in the air-only group reported a significant improvement in wellbeing, but objective scores did not reflect it. The authors suggested that the modest improvements seen in other studies may be due to a placebo effect.

How to read the conflicting results

The trials are not identical. The positive Israeli trial used 40 sessions; the two negative trials used 10. So the negative trials do not directly test the longer protocol. On the other hand, the evidence for the 40-session protocol comes from a single centre, and the Swedish and Belgian trials show how much people with long COVID can improve in a chamber even without extra oxygen. That placebo and participation effect is exactly why sham-controlled trials matter.

What do systematic reviews say?

  • A 2024 systematic review in Life found 10 clinical studies up to October 2023, including three completed randomised controlled trials. It noted that all three trials came from the same population at the same institution, and called for rigorous, large-scale trials.
  • A 2025 systematic review in Undersea and Hyperbaric Medicine included seven studies with 199 participants. It concluded that HBOT might be a potential and safe option, but that its efficacy needs testing in larger randomised studies.
  • The living systematic review in The BMJ (2024) looked at 24 randomised trials of all long COVID treatments, with 3,695 patients. It found moderate-certainty evidence that online cognitive behavioural therapy and a combined physical and mental health rehabilitation programme probably help. It found no compelling evidence for several other interventions, including hyperbaric oxygen. Its search ran to December 2023, before the Swedish and Belgian results were published.

Is HBOT safe for people with long COVID?

In the trials above, side effects were mostly mild and occurred at similar rates in the HBOT and sham or placebo groups. The Swedish trial reported one serious adverse event in the HBOT group.

Outside long COVID research, a review of HBOT side effects found that middle ear barotrauma (ear pain or damage from pressure changes) is one of the most common problems. Temporary short-sightedness has been reported in 25-100% of patients after several weeks of treatment at 2.0 ATA or higher, usually resolving within 3-6 weeks of stopping. Oxygen toxicity seizures are rare, at roughly 1 in 2,000-3,000 treatments. See our guide to HBOT side effects for more detail.

One more point: every trial above used medical hyperbaric chambers at 2.0 ATA or higher with 100% oxygen. Soft-shell "mild" chambers run at much lower pressures and oxygen levels, so these results do not apply to them. Our hard-shell vs soft-shell chamber guide explains the difference.

If you are still considering HBOT for long COVID

These questions will help you decide whether a particular offer is reasonable:

  1. Can I join a trial instead? A trial gives you monitoring and contributes to answering the question for everyone.
  2. What exactly is the protocol? Ask for the pressure, the oxygen percentage, session length and number of sessions, and which study it is based on.
  3. Who supervises treatment? Medical HBOT should be prescribed and supervised by a physician trained in hyperbaric medicine.
  4. How will we know if it is working? Agree on symptom questionnaires or tests before you start, and a point at which you stop if nothing changes.
  5. What does the whole course cost? Get the total price in writing before you commit. Insurers generally do not pay for off-label uses; our HBOT insurance coverage guide explains why.
  6. Does it fit with the rest of my care? Keep your long COVID doctor involved, especially if you have post-exertional symptom crashes, and continue rehabilitation that has evidence behind it.

If fatigue that worsens after exertion is your main symptom, our article on HBOT for chronic fatigue and fibromyalgia covers the overlap between long COVID and ME/CFS. For general advice on assessing providers, read how to choose an HBOT clinic, then use the directory to find a hyperbaric clinic near you.

Sources

This article is for information only and is not medical advice. Long COVID should be managed by qualified healthcare professionals, and whether HBOT is appropriate for you should be decided with a physician.

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