H2 antagonist or proton pump inhibitor is well advised to do oral B12 supplementation, especially if older than 50 years.

B12, like most proteins and protein-bound nutrients, needs the action of stomach acid to be broken out of food and absorbed, and people on these acid-reducing meds for significant periods of time do risk deficiencies, especially if they already may be predisposed.

I am, at least, seeing references to possible B12 deficiencies in the warnings about these meds lately.