For years patients with low blood counts due to low vitamin B 12 levels came in the office once a month for a Vitamin B12 injection. Two good studies compared intramuscular injection to oral route. Both forms raised low vitamin B12 levels and improved blood counts and neurologic symptoms. Both forms were well tolerated. The oral form was less expensive.
Recommendations per the US Centers for Disease Control and Prevention (CDC) are to give 1000 mcg daily by pill per mouth or intramuscular 1000 mcg monthly.
Take your pick.