Oral vitamin B12 replacement is as effective as intramuscular injections. According to this web site @ American Family Physicans.org. Go to web site below: Vitamin B12 Deficiency (American Family Physician March 1, 2003
Vitamin B-12 is a water soluble vitamin which means if you take more than your body needs it will just be excreted in the urine.
It is may have side effects but it's very unlikely that anyone would experience an overdose. Keep in mind Vitamin B-12 injectable is only given by prescription in the United States.
No toxic or adverse effects have been associated with large intakes of vitamin B12 from food or supplements in healthy people. Doses as high as 1 mg (1000 mcg) daily by mouth or 1 mg monthly by intramuscular (IM) injection have been used to treat pernicious anemia, without significant side effects. When high doses of vitamin B12 are given orally only a small percentage can be absorbed, which may explain its low toxicity. Because of the low toxicity of vitamin B12, no tolerable upper intake level (UL) was set by the Food
and Nutrition Board in 1998 when the RDA was revised. Per lpi.oregonstate.edu/infocenter/vitamins/vitaminB12/
There is a sub-linguinal form (under the tongue) you can buy it online www.sublingualb12.com They claim is absorbed better than oral,that info I'm not sure of. Injectable Vitamin B-12 is usually only used for those who have problems with absorption & usually when the Dr. prefers that method of replacement. Also B-12 levels are monitored thru blood tests. I have been on Cyanocobalamin injectable 1000mcgs. twice weekly for 5 months for true vitamin B-12 deficiency & the truth is I have not lost a pound. I wished it was a wt.loss med. cause I'm in the same boat as the rest of you. A little too much holiday ho-ho-ho. & then some.
A little more info.
Possible Side Effects of Injectable
CYANOCOBALAMIN (VITAMIN B-12) (Injection) (Injectable) Side Effects
Call your doctor right away if you notice any of these side effects:
Chest tightness or trouble breathing If you notice these less serious side effects, talk with your doctor:
Mild pain or irritation where the shot is given