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I swallow the sublinguals. They can really irritate the mouth IMO used under the tongue.

Injections only stay around for 72 hrs, so some people swing up and down with B12 especially when low.

Low levels also prevent the normal movement into the spinal cord and brain, and this confuses the enzyme systems that require methylB12 to work properly.

Some people cannot methylate cyano to the active form, and that is a genetic error that can be tested for. MTHFR DNA polymorphism test.
http://labtestsonline.org/understand...mthfr/tab/test

This genetic error is pretty common thought to be 10-30% of people! It also affects folic acid which needs to be methylated to methylfolate in the body to work.

You can ask your doctor for Metanx RX vitamin which has the active forms in it. Take that on an empty stomach.
And take your oral B12 on an empty stomach too for best absorption.

Only a few micrograms are absorbed from each daily dose (of 1000mcg), but this is what the body is used to so over time you will do better.
Our bodies were not designed to be flooded with injectable synthetic cyanocobalamin B12, so some people feel odd, or sense the swinging of the blood levels as unpleasant.