Table 1. In vivo H₂ delivery systems.

Administration	Preparation/delivery method	Characteristics
Inhalation	Inhale gas mixture containing H2 (< 4%) [1, 52–53]	1. Rapid action, straightforward delivery, but unsafe. 2. Does not influence blood physiological parameters (temperature, blood pressure, pH, pO2). 3. Suitable to defense against acute oxidative stress. 4. Unpractical to dose continuously.
Oral intake of hydrogen-rich water (HW)	Dissolving H2 in water up to 0.8 mM under atmospheric pressure at room temperature. Drinking HW [58, 63]	1. Convenient, easily administered, safe, efficient. 2. Easily evaporates and is lost in the stomach or intestine. 3. Difficult to control H2 concentration administered.
Injection of hydrogen-rich saline(HS)	Intravenous injection[122]	Delivery of more accurate H2concentrations.
	Intraperitoneal injection[25]
	Intrathecal injection [68]
	Intravitreal injection [201]
Direct incorporation	Bath [69]	1. Low cost. 2. Convenient and safe.
	Cold storage of transplanted organs [71]
	Eye drops [72]
	Spray on plants or immerse plants [22]
Increased intestinal hydrogen	Oral drugs (e.g. acarbose, lactulose)[88]	1. Low cost. 2. Convenient.
	Dietary(e.g. turmeric) [86]