Effectiveness and safety of hyperbaric oxygen therapy for psychiatric disorders: A systematic review and meta-analysis.

Psychiatric disorders such as major depressive disorder (MDD), posttraumatic stress disorder (PTSD), and anxiety are leading causes of disability and remain insufficiently treated in many patients. Hyperbaric oxygen therapy (HBOT), traditionally used in neurological care, has emerged as a potential intervention by delivering 100% oxygen at supra-atmospheric pressure to modulate neuroplasticity, inflammation, and cerebral perfusion. We conducted a systematic review and meta-analysis of studies evaluating HBOT in adults with psychiatric disorders across three databases. The prespecified primary endpoint was psychiatric symptom severity at treatment's end. Random-effects models were implemented in R (v4.4.0). Seventeen studies (n = 920) met inclusion criteria; nine randomized control trials (RCTs) contributed to the meta-analysis. For depressive symptoms, HBOT was associated with a large pooled effect (Cohen's d = -0.82; I2 = 82%). A clear dose-response was observed: robust benefit at 2.0 ATA (atmospheres absolute; d = -0.93) but none at 1.2 ATA. Subgroup analysis by comparator showed significant heterogeneity (P = 0.038): moderate effects versus sham (d = -0.68), large effects versus usual care/psychotherapy (d = -1.33), and no significant difference versus antidepressants (d = -0.60). For anxiety, three studies found a moderate effect (d = -0.59; I2 = 42.8%). Two sham-controlled RCTs in PTSD demonstrated a large effect (d = -1.96; I2 = 0%). Adverse events were mild and transient, mainly ear discomfort and brief anxiety. Evidence remains preliminary, but HBOT shows potential symptom benefits in MDD, anxiety, and PTSD, particularly at therapeutic dosing. However, effects are variable, estimates heterogeneous, and most studies small, highlighting the need for larger, rigorously designed RCTs with standardized protocols and long-term follow-up to establish its role in psychiatric care.