One injection a month is not enough. That is the old old treatment, found in the therapy books doctors use as a reference.

Injections last about 72 hrs, and the rest of the month there is nothing. Our bodies evolved to have "some" B12 every day. There is a cushion from the liver in case of famine that may last up to 5 yrs. Once this is depleted it may take years to rebuild and won't ever if you remain low daily.

Here is a link from this thread from the 1st post to a study showing absorption from various modes of administration based on blood levels:

http://www.ncbi.nlm.nih.gov/pmc/arti...able/T1/#TF1-4

Oral taken on an empty stomach, shows 13mcg/1000mcg administered. The RDA from food is about 2-4 micrograms.
So 1000mcg orally may give up to 13 absorbed. Multiply by 30 days and you have 390micrograms in your blood ideally per month.
Compared to one injection of 1000mcg yielding 150mcg absorbed for one dose only.

It is no wonder you feel low, after a few days from your shot. You ARE low.

With methylcobalamin being so available and inexpensive today, you don't need shots anymore! And most doctors don't even know what methylB12 is!

If you do the oral 5mg (because you are very deficient) for 6mons and get retested you can surprise your doctor mightily...it is worth it to get tested then and come back with a higher level than 1000 (which is what many here aim for).
Costs you pennies a day, too. Then YOU can educate your doctor and perhaps help other patients of his/her.