In short, the difference between oral supplementation and injection is that an injection will provide a higher dose of B12 at regular intervals, whilst oral supplements have a lower dosage and can be taken every day
If you follow a vegan diet, B12 is not found naturally in fruit, vegetables or grains, so fortified foods or a supplement matter more, and seaweed, spirulina and similar products are not reliable sources
Where deficiency is confirmed, treatment may include oral supplementation (for dietary insufficiency or mild malabsorption) or intramuscular hydroxocobalamin injections (for pernicious anaemia or severe malabsorption), as per NICE and British Society for Haematology guidelines
We will talk about this a little bit later, but it turns out that Vitamin B12 must go through several steps before it is properly absorbed through your GI tract and several hormone imbalances (including thyroid) can alter this absorption
Lipotropic B12 FAQs Who is qualified to receive B12 injections
project number 223269)