many antioxidants in the presence of transitional metals(iron or copper) are pro-oxidative.

Antioxidants like ascorbate (vitamin C) or polyphenols donate electrons to neutralize free radicals (e.g., •OH, O₂•⁻). However, in the presence of free transition metals (Fe²⁺/Cu⁺), they over-reduce these metals, initiating a catalytic cycle that generates more radicals than they scavenge.

this is why hydrogen water (although it appears scammy) is actually founded in biochemical truth in comparison to most exogenous antioxidants

hydrogen is not an antioxidant it is a reducing agent and can only donate an electron not catalyze other oxidative processes after donating itself.

it is far safer and probably healthier to drink a couple cups of "hydrogen" water than antioxidant supplements.