Why I Don’t Recommend B12 Injections

Despite the daily requirements for B12 being very low, B12 injections (containing high doses) are readily used as a treatment in cases if B12 deficiency. Just how sustainable or long term a solution this is in many cases, is questionable. In this article I explain two primary reasons for why as well as identify the circumstances that may warrant it.

Firstly, so as not to downplay the significance of B12, please know that it is a vitamin crucial to life. If B12 availability is lacking it can cause reversible anaemia, demyelinating neurologic disease, or both. It means the signs of B12 deficiency present as:

  • Numbness or tingling in the hands, legs or feet
  • Low energy
  • Cognitive difficulties
  • Memory loss
  • Weakness
  • Yellowing skin (jaundice)
  • Swollen or inflamed tongue

These symptoms progressively worsen over an extended period because the body is very good at recycling B12, thus a deficiency can take years to develop and for symptoms to emerge. 

1. Ongoing reliance

An individual being treated with B12 injections will often report an initial surge in energy and vitality post treatment and then a drop off which is usually what precedes the next injection. And so, the trend continues. 

The reason for this may be related to the passive diffusion of B12 into cells. For passive diffusion to occur there must be a steep concentration gradient, meaning elements move from areas of higher concentration to areas of lower concentration. In the case of B12 injections, the dose is far higher than daily requirements which is what allows blood levels of B12 to become very high and because the cells have significantly lower levels in comparison, B12 passes through the cell wall and into the cell. The cell is full! 

This gradient slope always needs to be maintained though, so as the blood levels decline post injection the concentration gradients work in the opposite direction and B12 can leave the cells. It’s when this happens that the initial feelings of vitality dissipate, and the next injection is administered.

2. It does not treat root cause

A B12 deficiency didn’t start with a lack of B12 injections. For long term resolution the root cause needs to be identified and the treatment needs to reflect this. Common causes of deficiency include:   

  • Hypochlorhydria (low stomach acid) as a result of gastrointestinal surgery, ageing, the use of medications including proton pump inhibitors and metformin and chronic stress. Hydrochloric acid is required to free B12 from the protein it’s bound to in food. 
  • Lack of Intrinsic Factor (IF). IF is a glycoprotein secreted by the parietal cells of the stomach and it supports B12 absorption in the small intestine. This can affect those that have had gastrointestinal surgery as well as individuals with a condition known as Pernicious Anaemia who often fail to produce IF and left untreated, it can result in B12 deficiency. 
  • Other disorders of the stomach and small intestine including coeliac disease and Crohn’s disease
  • B12 crosses the placenta during pregnancy and is present in breastmilk. Exclusively breastfed children of exclusively plant-based mothers (who may have limited B12 reserves) are therefore at risk of B12 deficiency within just months of birth. 
  • An exclusively plant based or largely plant-based diet, with little to no dietary B12 intake.

Next steps

  1. If you suspect you have a B12 deficiency, the first step is to create a baseline by getting tested. The tests we recommend include:
  • Homocysteine
  • Full blood count
  • Total B12
  • Holotranscobalamin
  • MMA

2. Determine the root cause for deficiency. In understanding this you can work with a practitioner to determine if your case requires an exogenous source of B12, what kind, how much and how long for. There are some cases that require supplementation, such as those that are driven by diet or lack of IF. Where the cause of B12 deficiency can be modified, such as medication and stress, we suggest addressing that before looking to an exogenous source. 

If you require support in addressing low B12 or suspect less than optimal B12 please don’t hesitate to book in for 15-minute Complimentary Consultation. 


Vidal-Alaball J, Butler CC, Cannings-John R, Goringe A, Hood K, McCaddon A, McDowell I, Papaioannou A. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database Syst Rev. 2005 Jul 20;(3):CD004655. doi: 10.1002/14651858.CD004655.pub2. Update in: Cochrane Database Syst Rev. 2018 Mar 15;3:CD004655. PMID: 16034940; PMCID: PMC5112015.

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