Does vitamin B12 give you energy?

Not unless you are short of it, as far as the trials can tell. A 2021 meta-analysis of 16 randomized trials in 6,276 people without clear B12 deficiency found just one trial that measured fatigue, too few to analyze. The best direct test, in 95 tired patients with normal B12, found 1000 ug a day for 8 weeks did no better than placebo. Fatigue is a known symptom of B12 deficiency, and that is the case where B12 belongs.

Unsettled. Whether extra B12 lifts tiredness in otherwise healthy people with normal levels has barely been tested. The one direct trial was in people with irritable bowel syndrome or inflammatory bowel disease. The products with small positive results mixed B12 with other vitamins, so nobody can say what B12 contributed.

What the trials found

B12 on its own, in people who are not deficient

The 2021 review looked for any randomized trial of B12 in people without advanced neurological disease or overt deficiency. It found 16 trials in 6,276 people. Only one reported fatigue, so no pooled answer was possible, and B12 had no effect on cognition or depression. In that single fatigue trial, B12 beat placebo on a vitality score only at week 8, and the placebo group already had better scores at the start. The reviewers call the evidence too sparse for conclusions.

The cleanest direct test came from the Netherlands. In 95 people with irritable bowel syndrome or inflammatory bowel disease, all tired and all with normal blood B12, 1000 ug a day for 8 weeks changed the fatigue score by -8.1 points, against -8.3 on placebo. The authors write that the trial did not confirm the expected effect.

Chronic fatigue syndrome

Myth. Vitamin injections and supplements have been tested in chronic fatigue syndrome, and they did not help. A systematic review of 5 randomized trials and 40 observational studies in chronic fatigue syndrome and fibromyalgia found the supplement trials produced no clinical improvement, on studies of poor quality. In a 1989 crossover trial of 15 patients, injections of liver extract with folic acid and B12 did no better than placebo shots, and the placebo response was strong.

That strong placebo response is worth keeping in mind when someone says a B12 shot made them feel better. In both direct trials above, people on placebo improved too.

Mixed vitamin products

A meta-analysis of 8 randomized trials in healthy people found multivitamin and mineral supplements taken for at least 28 days lowered fatigue ratings by a small amount, a standardized difference of 0.27 (95% CI 0.15 to 0.40). Because those products contained many nutrients, the effect cannot be credited to B12. In 98 adults with inflammatory bowel disease in remission, vitamins B1, B6 and B12 with magnesium for 4 weeks lowered fatigue scores (beta -1.98 and -5.19 on two sections of the scale, both p below 0.001), with no change in quality of life. Again, four ingredients went in together.

Other combination trials found nothing. In a 12 week trial in 202 people on hemodialysis, a drink of B vitamins, vitamin C, carnitine, CoQ10 and zinc did not change fatigue against placebo.

One small trial points the other way for physical tiredness. In 32 healthy adults aged 20 to 30, a supplement of vitamins B1, B2, B6 and B12 for 28 days increased running time to exhaustion 1.26-fold against placebo. That was a single trial of a commercial product, it measured a lab treadmill test and not everyday tiredness, and it sits against the NIH summary below.

When the tiredness is deficiency

Fatigue is one of the symptoms of B12 deficiency, along with nerve changes, a large-cell anemia, a sore tongue and palpitations, and the NIH notes these can take years to appear. Treatment works by mouth as well as by injection for blood levels. A Cochrane review of 3 trials in 153 deficient adults found oral and injected B12 normalized blood B12 to a similar degree, with oral treatment costing less, on low quality evidence. None of its trials reported on symptoms of deficiency, fatigue included.

Who should be careful

The Food and Nutrition Board set no upper limit for vitamin B12, because of its low potential for toxicity. That is a statement about safety, and it says nothing about benefit.

Not for everyone. Metformin and stomach acid blockers can lower B12. A meta-analysis of 4 trials in type 2 diabetes found metformin lowered blood B12 by 57 pmol/L (95% CI 35 to 79) after 6 weeks to 3 months. The NIH lists gastric acid inhibitors and metformin among medicines that may affect B12 levels. In people taking them, tiredness can be a sign of true deficiency, which is worth raising with the prescriber.

We have no card on B12 and fatigue in pregnancy, in vegans or vegetarians, or in older adults, so this page says nothing about those groups.

What expert bodies say

The NIH Office of Dietary Supplements notes that B12 is promoted as an energy booster and says supplements appear to have no benefit on performance in people without a deficit. That statement rests on two studies and is about athletic performance, so it does not directly address everyday tiredness. The NIH lists fatigue among the symptoms of deficiency.

The European Union authorizes the label claim that vitamin B12 contributes to the reduction of tiredness and fatigue. The register entry does not say what evidence it rests on, and it sits apart from the trials on this page, which found no benefit in people with normal levels. We could not get the NICE guideline on B12 deficiency, so this page cites no NICE position.

How we searched

What would change this answer

• A randomized trial of B12 alone in tired adults with normal levels and no bowel disease. That is the question most people ask, and nobody has tested it directly.
• Combination trials with a B12 only arm, so the small effects of multivitamin products could be credited to the right ingredient.
• A trial in deficient people that measured fatigue as an outcome, not only blood levels.
• Access to the 1973 pilot trial and the NICE guideline. The trial registry showed no trial of B12 for fatigue under way.

How much B12 you need, where it comes from and who runs short is in the vitamin B12 guide.

Sources

1. ev-b12f-01 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 6276
   Further, only one study reported effects on idiopathic fatigue, and therefore, no analysis was possible.
   
   Who: patients without advanced neurological disorders or overt vitamin B12 deficiency
   Effect: fatigue: 1 trial, no pooled estimate possible; cognition and depressive symptoms: no effect of B12 alone or B complex
   Certainty: The main synthesis for the question; the gap on fatigue is itself the finding.
   Nutrients, 2021 · checked 2026-10-07 · we read the abstract
2. ev-b12f-02 · Randomized controlled trial(s) · systematic review and meta-analysis of randomized controlled trials · n = 1 trial
   Moreover, there was already a statistically significant difference at baseline between the two groups with higher starting scores (=better) in the placebo group.
   
   Who: participants of the single RCT on idiopathic fatigue included in the review
   Effect: significant difference on SF-36 vitality subscale only at 8 weeks; placebo group had better baseline scores
   Certainty: Baseline imbalance makes the one positive signal unreliable; the authors call the evidence too sparse for conclusions.
   Nutrients, 2021 · checked 2026-10-07 · we read the fulltext
3. ev-b12f-03 · Meta-analysis or systematic review · meta-analysis of randomized placebo-controlled trials · n = 8 studies
   Fatigue (SMD=0.27; 95% CI=0.40-0.146; p<.001) and confusion (SMD=0.225; 95% CI=0.38-0.07; p<.003) were also reduced.
   
   Who: nonclinical samples, general population, multivitamin/mineral supplements for at least 28 days
   Effect: fatigue SMD 0.27 (95% CI 0.15 to 0.40, p<.001); perceived stress SMD 0.35; no significant effect on depression
   Certainty: Combined supplements, so the effect cannot be attributed to B12; small effect, self-rated mood scales.
   Psychosom Med, 2013 · checked 2026-10-07 · we read the abstract
4. ev-b12f-04 · Meta-analysis or systematic review · Cochrane systematic review of randomized controlled trials, no meta-analysis · n = 153
   Low quality evidence shows oral and IM vitamin B12 having similar effects in terms of normalising serum vitamin B12 levels, but oral treatment costs less.
   
   Who: adults with vitamin B12 deficiency, mean age 38.6 to 72 years, treated 3 to 4 months
   Effect: similar normalization of serum B12 with oral and IM; oral treatment costs less
   Certainty: Low quality evidence (GRADE); no included trial reported clinical signs and symptoms of deficiency, fatigue included.
   Cochrane Database Syst Rev, 2018 · checked 2026-10-07 · we read the abstract
5. ev-b12f-05 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs and observational studies · n = 45 studies
   In addition, RCTs testing supplements containing these vitamins and/or minerals did not result in clinical improvements.
   
   Who: chronic fatigue syndrome and fibromyalgia syndrome patients
   Effect: RCTs of vitamin and/or mineral supplements: no clinical improvement; no vitamin consistently linked to symptoms
   Certainty: Poor study quality and high heterogeneity; supplement RCT conclusion is qualitative.
   PLoS One, 2017 · checked 2026-10-07 · we read the abstract
6. ev-b12f-06 · Randomized controlled trial(s) · randomized double-blind placebo-controlled trial, 1000 ug/day oral B12, 8 weeks · n = 95
   This study did not confirm the expected effect of non-conventional surplus vit B12 supplementation on fatigue in IBS or IBD patients.
   
   Who: out-clinic IBS and IBD patients with deactivating fatigue and normal vitamin B12 blood levels (>=150 pmol/l) aged 18-65 years
   Effect: CIS subjective fatigue change -8.1 vs -8.3 with placebo (95% CI -11.65 to 6.71); motivation subscale -2.2 (95% CI -4.4 to -0.04)
   Certainty: The cleanest direct test of high-dose B12 for fatigue in people who are not deficient.
   Clin Nutr ESPEN, 2018 · checked 2026-10-07 · we read the abstract
7. ev-b12f-07 · Randomized controlled trial(s) · randomized double-blind placebo-controlled trial, 4 weeks · n = 98
   Compared with placebo, the intervention produced greater reductions in ulcerative colitis (UC) activity measured by P-SCCAI (β = -1.32; p = 0.006) and fatigue assessed by IBD-F Section 1 (β = -1.98; p < 0.001) and Section 2 (β = - 5.19; p < 0.001).
   
   Who: adults with IBD in remission
   Effect: IBD-F section 1 beta -1.98 (p<0.001), section 2 beta -5.19 (p<0.001); no effect on quality of life (IBDQ-9)
   Certainty: Combination product, so B12's share is unknown; deficiency status at baseline not stated in abstract; short follow-up.
   Sci Rep, 2026 · checked 2026-10-07 · we read the abstract
8. ev-b12f-08 · Randomized controlled trial(s) · double-blind placebo-controlled crossover trial of intramuscular injections · n = 15
   The placebo response appeared to be strong.
   
   Who: patients who met the Centers for Disease Control criteria for chronic fatigue syndrome
   Effect: no significant difference between LEFAC and placebo on functional status; strong placebo response
   Certainty: Tiny and old (1989); the strong placebo response matters for anecdotes about B12 shots.
   Arch Intern Med, 1989 · checked 2026-10-07 · we read the abstract
9. ev-b12f-09 · Randomized controlled trial(s) · randomized double-blind placebo-controlled multicentre trial · n = 202
   Clinical characteristics, changes in fatigue, quality of life score, endocrine functions, and laboratory data did not differ significantly between the two groups.
   
   Who: hemodialysis patients with end-stage renal disease
   Effect: no significant difference in fatigue or quality of life score between groups after 12 weeks
   Certainty: Multinutrient drink (B vitamins, C, carnitine, CoQ10, zinc), so not B12 alone.
   PLoS One, 2015 · checked 2026-10-07 · we read the abstract
10. ev-b12f-10 · Randomized controlled trial(s) · randomized double-blind crossover trial, 28 days · n = 32
    After supplementation with Ex PLUS®, we found a significant increase in the running time by 1.26-fold (p < 0.05) to exhaustion compared to that before supplementation and that in the placebo group.
    
    Who: sixteen male and sixteen female subjects, aged 20-30 years
    Effect: running time to exhaustion 1.26-fold (p<0.05); lower blood lactate and ammonia
    Certainty: Single small industry-product trial; physical fatigue in a lab test, not everyday tiredness; contradicts ODS summary.
    Int J Med Sci, 2023 · checked 2026-10-07 · we read the abstract
11. ev-b12f-11 · Position of an expert body · agency fact sheet · n = —
    However, vitamin B12 supplementation appears to have no beneficial effect on performance in the absence of a nutritional deficit [99,100].
    
    Who: people who have sufficient vitamin B12 status
    Effect: no beneficial effect on athletic performance or endurance in the absence of a nutritional deficit
    Certainty: Agency summary citing two studies; does not address everyday tiredness directly.
    NIH Office of Dietary Supplements, Vitamin B12 fact sheet for health professionals · checked 2026-10-07 · we read the section
12. ev-b12f-12 · Position of an expert body · agency fact sheet · n = —
    Vitamin B12 deficiency can cause a number of symptoms, including fatigue, neurological changes, megaloblastic anemia, glossitis of the tongue, palpitations, and low counts of white and red blood cells.
    
    Who: people with vitamin B12 deficiency
    Effect: symptoms include fatigue, neurological changes, megaloblastic anemia, glossitis, palpitations
    Certainty: Explains why B12 helps fatigue only when deficiency is the cause.
    NIH Office of Dietary Supplements, Vitamin B12 fact sheet for health professionals · checked 2026-10-07 · we read the section
13. ev-b12f-13 · Position of an expert body · agency fact sheet · n = —
    The FNB did not establish a UL for vitamin B12 because of its low potential for toxicity [1].
    
    Who: general population
    Effect: no UL set by the Food and Nutrition Board
    Certainty: Safety of high doses does not imply benefit.
    NIH Office of Dietary Supplements, Vitamin B12 fact sheet for health professionals · checked 2026-10-07 · we read the section
14. ev-b12f-14 · Position of an expert body · agency fact sheet · n = —
    Vitamin B12 supplements may interact with medications, and some medications, including gastric acid inhibitors and metformin, may affect vitamin B12 levels.
    
    Who: individuals taking gastric acid inhibitors or metformin on a regular basis
    Effect: reduced B12 absorption and serum levels
    Certainty: Relevant because tiredness in these groups may be true deficiency.
    NIH Office of Dietary Supplements, Vitamin B12 fact sheet for health professionals · checked 2026-10-07 · we read the section
15. ev-b12f-15 · Meta-analysis or systematic review · systematic review of 26 papers with meta-analysis of 4 trials · n = 4 trials
    Meta-analysis performed on four trials demonstrated a statistically significant overall mean B12 reducing effect of metformin of 57pmol/L [WMD (fixed)=-0.57 (95% CI: -35 to -79pmol/L)] after 6weeks to 3months of use.
    
    Who: patients with type 2 diabetes taking metformin
    Effect: mean B12 reduction 57 pmol/L (95% CI 35 to 79) after 6 weeks to 3 months
    Certainty: Pooled estimate from 4 trials; observational part supports it.
    Diabetes Metab, 2016 · checked 2026-10-07 · we read the abstract
16. ev-b12f-16 · Position of an expert body · EU health claims register entry · n = —
    POL-HC-6488 Vitamin B12 Vitamin B12 contributes to the reduction of tiredness and fatigue Authorised
    
    Who: EU food and supplement labeling
    Effect: authorized health claim; conditions of use (minimum content) in Regulation (EU) 432/2012, not quoted here
    Certainty: The register entry does not state its evidence base; it diverges from the NIH ODS summary and the trials in people with normal B12.
    EU Register on nutrition and health claims, claim POL-HC-6488, snapshot 2026-09-21 · checked 2026-10-07 · we read the section