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Does Vitamin B12 Give You Energy? Who Needs It, Pills vs Shots, and What the Trials Show

Vitamin B12 restores energy only if you are low in it. In 95 tired adults with bowel conditions (IBS or IBD) and normal B12, 1,000 mcg daily for 8 weeks eased fatigue no more than placebo (grade C), and 16 trials found no gain in memory or mood (grade A). If you are deficient, high-dose tablets raised B12 about as well as injections (grade B). Older adults, vegans and people on metformin or acid reducers should ask for a test.

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Vitamin B12 is sold as an energy supplement, but it only fixes tiredness that a shortage causes. Here is who runs low, how to find out, whether tablets or shots work better, what B12 does and doesn't do for energy, memory and mood, and where B-complex and "energy" blends can cause trouble.

The short version

  • Without a deficiency, B12 did not ease fatigue: 1,000 mcg daily over 8 weeks was no better than placebo for fatigue in 95 adults with irritable bowel syndrome or inflammatory bowel disease, fatigue and normal B12; only a motivation sub-score improved. Grade C (Scholten 2018).
  • Without a deficiency, B12 did not help memory, thinking or mood across 16 trials. Grade A for no benefit (Markun 2021).
  • If you are deficient, high-dose tablets raise B12 about as well as injections for most people. Grade B (Wang 2018; Abdelwahab 2024).
  • Long-term metformin makes running low more likely, about twice as likely across 31 studies. Grade B (Yang 2019; de Jager 2010).

Does vitamin B12 give you energy?

Only if you are low. Grade C for no benefit when levels are normal. In a double-blind trial, 95 adults with irritable bowel syndrome or inflammatory bowel disease, disabling fatigue and normal B12 took either 1,000 mcg of B12 or a placebo daily, for 8 weeks. Their main fatigue scores improved by the same amount in both groups; only a motivation sub-score improved slightly more on B12, and mood and quality of life did not change (Scholten 2018). A 2021 review looked for trials on unexplained tiredness and found only one, too few to pool (Markun 2021).

A real deficiency is different. Low B12 can cause tiredness, brain fog, low mood, numb or tingling feet and unsteady walking, and correcting it eases those symptoms (Patel 2025). That is why a test comes first: the same tiredness has many other causes, from poor sleep to low iron or an underactive thyroid.

Does B12 help memory or mood if your levels are normal?

No. Grade A for no benefit. Across 16 randomized trials (6,276 people without a deficiency or advanced nerve disease), B12 alone or with folic acid and B6 did not improve any area of memory or thinking, and did not improve depression scores (Markun 2021). Our database grades these outcomes D from single rows; we give A because a meta-analysis of 16 trials points the same way. In people with heart disease and high homocysteine (an amino acid B vitamins lower), B12 did not cut heart attacks or strokes or slow mental decline (Langan 2017).

Who should get their B12 checked?

About 2% to 3% of US adults are deficient, and testing everyone isn't recommended. Testing makes sense when you have a risk factor and a symptom (Patel 2025). Risk factors in family-medicine guidance include (Langan 2017):

  • Metformin for more than 4 months. In 31 studies, people with diabetes on metformin had about twice the risk of B12 deficiency, more with higher doses and longer use (Yang 2019). See does metformin lower vitamin B12? for the label advice.
  • Acid-reducing medicines (PPIs or H2 blockers) for more than 12 months. In 25 studies, PPI users had about 1.4 times the odds of deficiency, though the authors called the link weak and most studies found similar B12 levels (Choudhury 2023). Grade C.
  • A vegan or strict vegetarian diet. In 40 studies, deficiency was common among vegetarians and most common among vegans who took no B12 (Pawlak 2014).
  • Age over 75, stomach or bowel surgery, or inflammatory bowel disease (Langan 2017).

A blood B12 below 180 pg/mL confirms a deficiency; a borderline result (180 to 350 pg/mL) needs a follow-up test called methylmalonic acid (Patel 2025). Ask for the test before you start supplements, so the result reflects your own level.

Are B12 tablets as good as shots?

For most people, yes. Grade B. A Cochrane review of 3 trials (153 people with a deficiency) found that taking 1,000 mcg daily as tablets brought blood B12 up about as far as injections did over 3 to 4 months, and a trial of 2,000 mcg a day did better than the shots; the evidence was low quality (Wang 2018). A 2024 analysis of 13 studies (4,275 people) found no significant difference between tablets, under-the-tongue forms and injections (Abdelwahab 2024). Family-medicine guidance says 1 to 2 mg (1,000 to 2,000 mcg) a day by mouth works as well as injections for anemia and nerve symptoms, while injections work faster and suit severe deficiency or serious nerve symptoms (Langan 2017). Injections and their schedule are your clinician's call. There is no upper limit for B12, because even large amounts are generally considered safe (NIH ODS).

Does B12 help numb or tingling feet?

Grade B in diabetic nerve damage. Pooling 6 trials in people with diabetic neuropathy (nerve damage from diabetes), B12 alone or combined with other treatments eased nerve symptoms and pain more than control, though a measure of vibration sense did not change (Karedath 2022). New numbness or tingling needs a diagnosis first, because a B12 shortage is only one cause.

Is a B-complex better than B12 alone for energy?

Not shown. Grade C. In a crossover trial of 32 healthy adults aged 20 to 30, a B-complex tablet for 28 days lengthened running time to exhaustion by 1.26 times compared with placebo; it tested one maker's product, and we found no second trial (Lee 2023). B-complex products also add folic acid and other B vitamins at doses that can matter. Upper limit for adults: 1,000 mcg of folic acid a day, because more can mask B12 deficiency; take more only with blood tests or your clinician's advice (NIH ODS; check your stack).

What we'd skip

  • B12 pills or shots for tiredness when your level is normal. No benefit over placebo in the trial that tested it (Scholten 2018).
  • B12 for memory or mood without a deficiency (Markun 2021).
  • High-dose B-vitamin combinations with kidney disease from diabetes. In 238 people, a tablet of folic acid, B6 and B12 sped up kidney decline and doubled heart attacks, strokes and deaths combined, compared with placebo (House 2010).
  • Paying more for methylcobalamin. Our B12 deficiency protocol found no trial showing it beats the common form, cyanocobalamin, and the tablet-versus-shot trials above used ordinary forms.

Safety and interactions

  • Biotin is not B12. Some B-complex and "energy" blends also contain biotin (vitamin B7). When 13 adults took biotin, 10 mg daily, some lab machines gave false thyroid results, worst 2 hours after a dose (Ylli 2021). Read does biotin affect thyroid and troponin tests? and tell the lab what you take.
  • Folic acid hides B12 deficiency. It can correct the anemia while nerve damage carries on, which is why it has an upper limit (NIH ODS).
  • A very high B12 on a test without supplements (above 1,000 pg/mL twice) has been linked to some cancers and heart deaths, so ask your clinician about it rather than ignoring it (Patel 2025).
  • Metformin or acid reducers: don't stop them on your own; ask your prescriber whether you need a B12 test.
  • Several supplements at once: check your stack against the upper limits. Pregnant, breastfeeding or for a child: ask a clinician.

When to see a doctor

  • Tiredness that lasts weeks, especially with pale skin, breathlessness, a sore red tongue or a racing heart.
  • Numbness, tingling, unsteady walking, or memory problems, which can come from low B12 even without anemia (Patel 2025).
  • You take metformin or an acid reducer long term, eat no animal foods, are over 75, or have had stomach or bowel surgery and haven't been tested (Langan 2017).

FAQ

Does vitamin B12 give you energy? Only if you are deficient. In 95 adults with irritable bowel syndrome or inflammatory bowel disease, fatigue and normal B12, 1,000 mcg daily over 8 weeks eased fatigue no more than placebo; only a motivation sub-score improved (grade C).

Are B12 shots better than pills? For most people with a deficiency, no: a Cochrane review found high-dose tablets matched injections for raising B12 (grade B). Shots work faster and suit severe deficiency or nerve symptoms.

Who should take vitamin B12? People with a confirmed deficiency, and those at risk who are advised to by a clinician: vegans, long-term metformin or acid-reducer users, people over 75 and people who have had stomach or bowel surgery.

Can you take too much vitamin B12? No upper limit has been set, because even large amounts are generally considered safe. Folic acid, often sold with it, does have an upper limit of 1,000 mcg a day.

Does B12 help memory or depression? Not without a deficiency: 16 trials with 6,276 people found no benefit (grade A).

Sources

  1. Scholten AM, et al. Surplus vitamin B(12) use does not reduce fatigue in patients with Irritable Bowel Syndrome or inflammatory bowel disease: A randomized double-blind placebo-controlled trial. Clin Nutr ESPEN. 2018. PubMed 29460813 · doi:10.1016/j.clnesp.2017.10.004
  2. Markun S, et al. Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue: A Systematic Review, Meta-Analysis, and Meta-Regression. Nutrients. 2021. PubMed 33809274 · doi:10.3390/nu13030923
  3. Wang H, et al. Oral vitamin B(12) versus intramuscular vitamin B(12) for vitamin B(12) deficiency. Cochrane Database Syst Rev. 2018. PubMed 29543316 · doi:10.1002/14651858.CD004655.pub3
  4. Abdelwahab OA, et al. Efficacy of different routes of vitamin B12 supplementation for the treatment of patients with vitamin B12 deficiency: A systematic review and network meta-analysis. Ir J Med Sci. 2024. PubMed 38231320 · doi:10.1007/s11845-023-03602-4
  5. Yang W, et al. Associations between metformin use and vitamin B(12) levels, anemia, and neuropathy in patients with diabetes: a meta-analysis. J Diabetes. 2019. PubMed 30615306 · doi:10.1111/1753-0407.12900
  6. de Jager J, et al. Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial. BMJ. 2010. PubMed 20488910 · doi:10.1136/bmj.c2181
  7. Choudhury A, et al. Vitamin B12 deficiency and use of proton pump inhibitors: a systematic review and meta-analysis. Expert Rev Gastroenterol Hepatol. 2023. PubMed 37060552 · doi:10.1080/17474124.2023.2204229
  8. Patel H, et al. Vitamin B12 Deficiency: Common Questions and Answers. Am Fam Physician. 2025. PubMed 40961307
  9. Langan RC, et al. Vitamin B12 Deficiency: Recognition and Management. Am Fam Physician. 2017. PubMed 28925645
  10. Pawlak R, et al. The prevalence of cobalamin deficiency among vegetarians assessed by serum vitamin B12: a review of literature. Eur J Clin Nutr. 2014. PubMed 24667752 · doi:10.1038/ejcn.2014.46
  11. Karedath J, et al. The Impact of Vitamin B12 Supplementation on Clinical Outcomes in Patients With Diabetic Neuropathy: A Meta-Analysis of Randomized Controlled Trials. Cureus. 2022. PubMed 36457818 · doi:10.7759/cureus.31783
  12. Lee MC, et al. A functional evaluation of anti-fatigue and exercise performance improvement following vitamin B complex supplementation in healthy humans, a randomized double-blind trial. Int J Med Sci. 2023. PubMed 37786445 · doi:10.7150/ijms.86738
  13. House AA, et al. Effect of B-vitamin therapy on progression of diabetic nephropathy: a randomized controlled trial. JAMA. 2010. PubMed 20424250 · doi:10.1001/jama.2010.490
  14. Ylli D, et al. Biotin Interference in Assays for Thyroid Hormones, Thyrotropin and Thyroglobulin. Thyroid. 2021. PubMed 34042535 · doi:10.1089/thy.2020.0866