Table 2.

Current H₂ therapy methods.

Method	Advantages	Disadvantages	Preparation Method	Administration Method	Ref.
H2 gas	Rapid and reliable	Risk of explosion, requires strict management and monitoring	Prepared using H2 generators	Direct inhalation of H2 gas under professional guidance	[2,74]
	Insignificant effect on blood pressure	Inconveniences during usage
HRW/HRS	Simple administration through drinking or injection, easily accepted by patients	Limited storage and duration in the body, limited treatment effect	H2 gas injection under high pressure	Oral ingestion or drinking, controlled dosage and frequency as per medical advice	[36,38,56,75,76,77,78,79,81]
	Partly mitigates the risk of direct H2 gas usage		Reaction between metals and water	Injection under professional healthcare personnel
			Electrolysis to produce HRW/HRS	Through drip infusion, controlled drip rate and dosage
				Local eye drops
H2 produced by intestinal bacteria	Production of H2 by intestinal bacteria, providing longer duration of effect	Variability due to individual differences in gut microbiota affecting H2 production	Induced by ingesting non-digestible substances	Through normal dietary intake of non-digestible components	[82,84]

Abbreviations: H₂, molecular hydrogen; HRS, hydrogen-rich saline; HRW, hydrogen-rich water.