B12 injections: who actually needs them and how often?

Vitamin B12 injections have become one of the most-googled wellness treatments in the UK, sold for everything from tiredness to brain fog to weight loss. The clinical reality is much narrower than the marketing. The NHS uses B12 injections for one thing: treating a proven vitamin B12 deficiency that the gut cannot fix on its own.

That is also our position at CoLaz. Below is a clinician’s view of who actually needs B12 injections, how often, what the NHS will and will not do for you, and what we check before we book the first shot.

What is vitamin B12 and where do you get it?

Vitamin B12 is a water-soluble vitamin your body uses to make red blood cells, maintain a healthy nervous system, and release energy from food. You cannot make B12 yourself; you have to get it from food or a supplement.

The natural sources are all animal-derived: meat, fish, eggs, milk and cheese. The NHS adult daily requirement is 1.5 micrograms a day, which a normal mixed diet covers easily and stores in the liver for years.

The catch is that B12 is one of the few nutrients you cannot get from an unfortified plant diet. People on vegan or strict plant-based diets need a reliable source from fortified foods (nutritional yeast, fortified plant milks, certain breakfast cereals) or a supplement. The Vegan Society recommends fortified foods three times a day, or a 10 microgram daily oral supplement, or a 2,000 microgram weekly oral supplement. For most vegans, those options work without ever needing an injection.

Who actually needs B12 injections?

B12 injections are needed when the gut cannot absorb dietary B12 properly, or when oral B12 alone is not enough to correct the deficiency. The biggest single cause in the UK is autoimmune gastritis, the condition older guidance called pernicious anaemia.

The 2024 NICE NG239 guideline on vitamin B12 deficiency in over-16s lists the main groups who need injections:

• Autoimmune gastritis (pernicious anaemia). The immune system attacks intrinsic factor, the stomach protein needed to absorb B12. Oral B12 cannot get into the bloodstream in normal doses. This is lifelong.
• Gastric surgery or bowel resection that has removed the part of the gut where B12 is absorbed.
• Crohn’s disease or coeliac disease with significant ileal involvement.
• Long-term use of metformin, proton pump inhibitors or H2 blockers, which can reduce B12 absorption over years.
• Long-term untreated vegan diet where deficiency has progressed beyond what oral replacement can comfortably catch up.
• Older adults with food-cobalamin malabsorption, where the stomach acid needed to release B12 from food has dropped with age.

If you do not fit one of those groups, the honest clinical answer is that you almost certainly do not need an injection. A blood test through your GP is the first step, not a private clinic.

What are the symptoms of B12 deficiency?

The classic symptoms of B12 deficiency are persistent fatigue, tingling or numbness in the hands and feet, problems with memory and concentration, mouth ulcers, a sore red tongue, and pale or yellow-tinged skin. They build up slowly over months.

The NHS symptoms list groups them into general anaemia symptoms (tiredness, breathlessness, headaches, loss of appetite, weight loss) and neurological signs (peripheral neuropathy, balance problems, depression, memory and concentration changes, sometimes mood changes or psychosis in advanced cases).

The 2024 NICE update was explicit on one point: do not rule out B12 deficiency just because the standard blood count looks normal. The NICE recommendations tell GPs to consider testing in anyone with one symptom or one risk factor, and to treat early to prevent neurological damage that can become permanent.

A 2025 European Journal of Clinical Nutrition commentary on the NICE guideline argued that the diagnostic threshold and clinical awareness still need to be tightened further, especially around pernicious anaemia, which is still under-recognised in primary care.

If you have several of those symptoms, please see your GP for a blood test. We do not perform diagnostic blood tests at CoLaz, and a private injection on top of an untested deficiency picture is not the right starting point.

How often are B12 injections given?

The NHS schedule for treating B12 deficiency is a loading dose of 1mg hydroxocobalamin by intramuscular injection every two to three days for two weeks, then a maintenance dose every two to three months for life when the cause is non-dietary.

The NHS treatment page lays it out clearly:

• Loading phase (no neurological symptoms): 1mg every other day for two weeks, or until symptoms stop improving.
• Loading phase (with neurological symptoms): 1mg on alternate days until there is no further improvement, then every two months.
• Maintenance, non-dietary cause: 1mg every two to three months for life.
• Maintenance, dietary cause: oral tablets or twice-yearly injections; many patients do well on a daily 50-150 microgram oral cyanocobalamin instead.

Hydroxocobalamin is the form the NHS uses because it lingers in the body longer than cyanocobalamin. Both forms work; the dosing schedule differs.

A subset of patients on standard NHS maintenance feel their symptoms return well before the next scheduled injection. The Pernicious Anaemia Society notes this is well documented but poorly understood, and that some patients self-inject more frequently. That is a conversation to have with your GP or a specialist haematologist, not a reason to add a private injection on top of an NHS schedule without telling either provider.

What about B12 shots for energy or weight loss?

The wellness positioning of B12 shots as an energy or weight-loss boost for healthy people is not supported by the NHS, by NICE, or by published trial evidence. If you are not deficient, a B12 injection does not add measurable energy or speed up weight loss.

B12 helps release energy from food, so a person whose blood levels are genuinely low can feel a real lift once treated. That is a deficiency being corrected, not a boost above normal. Once your blood B12 is in the normal range, more B12 does not produce more energy; the surplus is excreted.

The same logic applies to weight loss. There is no good evidence that B12 injections accelerate fat loss in people with normal B12 levels. Where you see weight-loss B12 protocols marketed (especially in the United States), they are almost always paired with calorie restriction and other interventions doing the actual work.

We will not sell a course of B12 injections on the energy or weight-loss claim, full stop.

How safe are B12 injections?

B12 injections are very safe when given by a trained clinician using sterile technique. Hydroxocobalamin has a long safety record, no meaningful overdose risk because excess is excreted in urine, and a very low rate of allergic reactions.

The main practical risks are:

• Injection-site soreness, bruising or mild redness, which settles within a day or two.
• Allergic reaction, rare but possible, particularly to the cobalt component of cobalamin. We screen for this at consultation.
• Hypokalaemia (low blood potassium) in the first weeks of loading-dose treatment in patients who started severely deficient. This is well known to clinicians and easily monitored.
• Mismanagement risk. Injecting B12 on top of an undiagnosed cause masks the underlying deficiency picture and can delay diagnosis of pernicious anaemia. This is the bigger risk and it is the reason we insist on a written history first.

Allergic and clinical risks are the reason every B12 injection at CoLaz is given by a clinician trained in injection technique and emergency response, working under written protocols. Look for that wherever you book, and check the practitioner is on the JCCP register.

Are vegans the same as B12-deficient?

Long-term vegans are at higher risk of B12 deficiency, but vegan does not equal deficient. Most vegans who use fortified foods or a daily supplement maintain normal B12 levels without ever needing an injection.

The NHS Inform Scotland guidance and the Vegan Society’s recommendation align: a 10-microgram daily B12 supplement, or a 2,000-microgram weekly supplement, is enough for the vast majority of plant-based eaters. Injections only enter the picture if a vegan has progressed to symptomatic deficiency, or has an absorption problem unrelated to diet.

If you have been vegan for several years without consistent B12 fortification, a GP blood test is the sensible starting point. If you are deficient, the NHS will treat you. If you are borderline, an oral supplement and dietary adjustment will usually catch you up faster than a private injection course.

How does CoLaz approach B12 injections?

At CoLaz, B12 injections are delivered by trained clinicians after a written consultation that screens medical history, medications, current symptoms and (where the picture warrants it) an NHS blood test through your GP. We do not give B12 injections on demand without a written reason.

In practice that means three things. First, if you have proven deficiency under NHS care and want a private top-up injection between NHS doses because your symptoms return early, we will do that on agreed protocol after seeing your blood results. Second, if you are vegan and asymptomatic, we will recommend oral supplementation first and only inject if there is a clinical reason. Third, if you have symptoms of deficiency that have never been investigated, we will tell you to see your GP for a blood test before we book anything.

That is not the most commercial position, and it is the one we believe a properly run aesthetic clinic owes its patients. If you want a written, no-obligation review of whether B12 injections or wider vitamin injections are the right answer for you, book a free consultation at any of our seven UK clinics.