Actually, it is quite common for people low in B12 to have an obvious response to oral B12 within days to a couple of weeks. Several days is quite common. It is absolutely not the case that it takes at least a month or two.

As a matter of fact, even if one were using the far less efficient cyanocobalamin orally, the response would usually be in far less time than that.

It is more complicated than it sounds. The dose one gets with a shot of cyanocobalamin must be converted to usable B12, and then a portion of that smaller amount is stored or used, and the balance goes out with the urine.

One who malabsorbs severely does get a smaller amount with a day's oral dose of 1000 mcg, but it is taken every day and there is not the gap between doses (most generally a month when being treated by a physician). The person taking an oral dose is being exposed to B12 every day and has an opportunity every day to store some.

And, when methylcobalamin is taken there is no need for the body to convert, so more is delivered.

In addition to all of that, there are individual differences. A person who does better on shots over the long run would be rare.

rose