Vitamin B complex: what it does, who needs B12, and why B6 now comes with a warning

Short answer

A vitamin B complex contains the eight B vitamins your body uses to turn food into energy, make red blood cells and keep nerves healthy. If you eat a varied diet, you probably get enough of most of them already. A B complex does not give you extra energy unless you are low in one of them.

The B vitamin people most often lack is B12. Older adults, vegans and vegetarians, people taking metformin or long-term acid-reducing medicines and people with gut conditions are at higher risk (1). B12 deficiency can cause tiredness, anaemia, numbness, tingling and memory problems.

For stress, a 2019 meta-analysis of 16 trials found that B vitamin supplements slightly reduced perceived stress, but did not reduce anxiety and had no significant effect on depressive symptoms (2).

The important warning is about vitamin B6. Too much B6 can damage nerves, causing tingling, burning or numbness in the hands and feet. The European Food Safety Authority lowered its safe upper limit to 12 mg a day in 2023 (3). Australia's medicines regulator has recorded about 250 reports of nerve problems linked to B6 products (4). Many B complexes, energy products and "magnesium with B6" supplements contain 25–100 mg.

If you have been taking a B complex for tiredness and still feel exhausted, you are not imagining it and it is not a failure of willpower. Persistent fatigue has many causes, and a supplement is rarely the whole answer.

Note: this article is for general education and is not medical advice. If you have numbness, tingling or burning in your hands or feet, stop B6-containing supplements you take on your own and talk to a doctor; if B6 was prescribed, ask your doctor before stopping.

What the B vitamins are and what they do

The B vitamins are a group of eight water-soluble vitamins. They often work together, which is why they are sold as a "complex", but each has its own job (1).

What does vitamin B complex do? In simple terms, the B vitamins act as helpers (coenzymes) in the chemical reactions that release energy from food and build cells. They do not contain energy themselves. That is why taking more than you need does not make you more energetic.

Because they are water-soluble, the body stores little of most B vitamins, and the excess leaves in urine. That is why a B complex can turn your urine bright yellow: that is riboflavin (B2), and it is harmless. The two important exceptions are B12, which the liver stores for years, and B6, which can build up to harmful levels from supplements.

B complex benefits: what the evidence shows

B complex benefits are real in specific situations and small or absent in others.

Clear benefit: correcting deficiency. If you are low in one or more B vitamins, supplements fix it and the symptoms it causes. This is the main reason to take them.

Stress: a small effect. The 2019 meta-analysis by Young and colleagues pooled 16 trials with 2,015 participants, mostly taking multivitamin and mineral products. B vitamins reduced perceived stress by a small amount (standardised effect size 0.23). There was no effect on anxiety and the effect on depressive symptoms was not significant. Benefits were more likely in people with a poor diet or low mood to begin with (2). The authors noted industry funding, and none of the participants were clinically deficient at the start.

B vitamins for energy: only if you are low. Fatigue is a classic symptom of B12 and folate deficiency, and fixing the deficiency helps. In people with normal levels, there is no good evidence that a B complex improves energy. If you are always tired, our guide to fatigue covers the more common causes.

Migraine: riboflavin (B2). High-dose riboflavin, 400 mg a day, is one of the supplements with some evidence for preventing migraine. US headache guidelines rated it "probably effective", but the trials are few and small: in one trial of 55 adults, it cut attacks by about two a month compared with placebo (8). It is not the same as a standard B complex, which contains much less. See our overview of migraine treatment.

Heart disease: no. Lowering homocysteine with B vitamins did not reliably reduce heart attacks. High-dose niacin, once used to improve cholesterol, did not reduce heart events in large trials when added to statins and caused more side effects, so it is no longer recommended for that purpose.

Hair, skin and nails: biotin and B complexes help only if you are deficient, which is rare. We cover this in our article on supplements for skin and hair.

Vitamin B12: the one many people need

Vitamin B12 benefits come down to two jobs: making healthy red blood cells and keeping nerves working. Adults need 2.4 mcg a day (1). B12 is found naturally only in animal foods, so vegans need a supplement or fortified foods.

Who is at risk of B12 deficiency:

• adults over 50, who absorb B12 from food less well because of reduced stomach acid;

• vegans and many vegetarians;

• people taking metformin for diabetes or PCOS for a long time;

• people taking proton pump inhibitors (such as omeprazole) or H2 blockers for a long time;

• people with pernicious anaemia, an autoimmune condition that blocks B12 absorption;

• people with coeliac disease, Crohn's disease or after weight-loss surgery or bowel surgery;

• heavy alcohol use.

B12 deficiency symptoms develop slowly, often over years, because the liver holds large stores:

• tiredness, weakness and shortness of breath;

• pale or slightly yellow skin;

• a sore, red tongue and mouth ulcers;

• numbness, tingling or "pins and needles" in the hands and feet;

• balance problems and difficulty walking;

• memory problems, confusion, low mood or irritability;

• vision changes in severe cases.

Nerve symptoms can appear even before anaemia, and if deficiency goes on too long, nerve damage can become permanent. That is why B12 is worth checking early if you are in a risk group. High doses of folic acid can hide B12 deficiency by correcting the anaemia while nerve damage continues; we explain this in our article on folate and folic acid.

B12 for energy. If you are deficient, B12 treatment can make a big difference to energy within weeks. If your levels are normal, extra B12 will not.

B12 injections vs tablets

B12 injections are used for severe deficiency, nerve symptoms and pernicious anaemia, where absorption from the gut is very poor. For many other people, high-dose oral B12 (often 1,000–2,000 mcg a day) works just as well, because a small fraction is absorbed without the normal stomach mechanism. A Cochrane review found that high-dose oral B12 raised blood levels similarly to injections in people with deficiency (5). Your doctor will choose based on the cause and severity.

"Energy" B12 injections offered at wellness clinics to people without deficiency have no proven benefit. B12 is very safe, and no upper limit has been set, but unusually high blood B12 without supplements can occasionally point to a liver or blood condition and should be checked.

Vitamin B6: benefits and the new safety concerns

What B6 does

Vitamin B6 helps the body use protein, make neurotransmitters such as serotonin and dopamine, and form red blood cells. Adults need about 1.3–1.7 mg a day, easy to get from a normal diet. True B6 deficiency is uncommon and usually occurs with other deficiencies, kidney disease, heavy alcohol use or certain medicines such as isoniazid.

Vitamin B6 benefits with evidence:

• Nausea in pregnancy: the American College of Obstetricians and Gynecologists recommends B6 as a first option for morning sickness, sometimes combined with an antihistamine (7). The dose should be agreed with your doctor or midwife, because it can approach the upper limit.

• Correcting deficiency.

Weaker or unproven uses include PMS (small, low-quality studies), carpal tunnel syndrome, mood and energy in people who are not deficient.

Vitamin B6 toxicity: why regulators are acting

Vitamin B6 toxicity causes peripheral neuropathy: damage to the nerves in the hands and feet. High intakes of B6 from food have not been reported to cause harm; the problem comes from supplements (7).

For decades, B6 nerve damage was thought to need very high doses, hundreds or thousands of milligrams. But reports at much lower doses have led regulators to act:

• European Union. In 2023, the European Food Safety Authority cut the tolerable upper intake level for adults from 25 mg to 12 mg a day from all sources (3).

• Australia. Since 2022, products with more than 10 mg of B6 per daily dose must carry a warning to stop taking them if you experience tingling, burning or numbness. As of October 2025, the Therapeutic Goods Administration had received 250 reports of peripheral neuropathy linked to B6 products, and from June 2027 products with 50–200 mg will be available only from a pharmacist (4).

• Netherlands. The national pharmacovigilance centre recorded 238 cases of nerve damage linked to B6 products between 2007 and 2024; 79 involved daily doses of 12 mg or less (6).

• United Kingdom advises no more than 10 mg a day from supplements unless a doctor recommends more. Canada now expects warnings on products with 10 mg or more (6).

• United States. The upper limit is still 100 mg a day, set in 1998 (7).

There is real scientific debate. Industry groups argue that neuropathy in good-quality studies usually appears above 200 mg a day and that some low-dose reports are poorly documented (6). Sensitivity also seems to vary widely between people. But the direction of travel is clear: more regulators now treat long-term B6 doses above about 10–12 mg as worth avoiding without a medical reason.

Vitamin B6 toxicity symptoms

Vitamin B6 toxicity symptoms usually appear gradually and symmetrically:

• tingling, "pins and needles", burning or numbness in the feet and hands;

• pain or increased sensitivity to touch;

• unsteady walking or poor balance, especially in the dark;

• muscle weakness in more severe cases;

• sometimes skin sensitivity to sunlight or nausea.

Confusingly, these symptoms resemble B6 or B12 deficiency, so people sometimes take more B vitamins to treat them, which makes things worse (4). Most people improve after stopping B6, though recovery can take months and is sometimes incomplete.

Where too much B6 comes from

Too much B6 usually comes from stacking several products, each of which looks harmless on its own:

• B complex and "stress" formulas, often 25–100 mg per tablet;

• magnesium supplements with B6, popular for sleep and cramps (see our article on magnesium glycinate for sleep);

• multivitamins, zinc products and PMS formulas;

• energy drinks and "hangover" products;

• fortified foods.

Labels can list B6 as pyridoxine hydrochloride, pyridoxal 5-phosphate (P5P) or pyridoxamine, so it is easy to miss. Some researchers think the active P5P form may be less likely to cause neuropathy, but this is not established.

A practical check: add up the B6 in every supplement you take. If the total is above about 10–12 mg a day and you do not have a medical reason, ask your doctor or pharmacist whether you need that much.

Other B vitamins worth knowing about

Thiamine (B1). Deficiency is mostly seen with heavy alcohol use, severe vomiting (including in pregnancy), after weight-loss surgery and in malnutrition. It can cause serious nerve and brain problems, and treatment is urgent.

Niacin (B3). High doses cause flushing, itching, stomach upset and, at the highest doses, liver injury and higher blood sugar. Do not take high-dose niacin without medical supervision.

Biotin (B7). High-dose biotin, common in hair and nail products, can distort blood tests, including thyroid tests (10) and troponin, a key test for heart attacks (9). Tell your doctor and the lab if you take it.

B complex vitamin side effects

At normal doses, most B complexes are safe. B complex vitamin side effects can include:

• bright yellow urine (harmless, from B2);

• stomach upset or nausea;

• flushing from niacin;

• nerve symptoms from long-term B6 at high doses;

• distorted lab tests from high-dose biotin.

People with kidney disease, those who are pregnant and anyone taking anti-seizure medicines, theophylline or cycloserine (7), levodopa or methotrexate should check B vitamin supplements with a doctor or pharmacist. Do not stop or change a prescribed medicine because of a supplement without talking to your doctor.

Living with B vitamins: the questions people ask next

Should I take a B complex every day?

Only if you have a reason: a diagnosed deficiency, a diet that excludes animal foods, a medicine or condition that affects absorption, or pregnancy. If you take one, choose a product with no more than about 10 mg of B6 unless your doctor advises more.

Is it safe to take B12 every day?

For most adults, yes. No upper limit has been set because B12 has a low potential for harm (1), and excess is excreted. If you take prescription medicines, check with your pharmacist. Daily B12 is recommended for vegans and many older adults.

How long does it take for B vitamins to work?

If you are deficient, energy and mood can start improving within days to weeks of treating B12 deficiency, while nerve symptoms take months. If you are not deficient, you are unlikely to notice a difference.

Can B vitamins cause anxiety or trouble sleeping?

Some people report feeling wired or sleeping poorly after taking B vitamins late in the day, though evidence is limited. Taking them in the morning with food is a simple fix.

My magnesium contains B6. Is that a problem?

Check the amount. Many "magnesium plus B6" products contain 5–20 mg of B6 per dose, and taking two doses or combining them with a B complex can push you well above 12 mg.

Can I test my B vitamin levels?

Yes. B12 (often with methylmalonic acid if borderline), folate, and in specific cases B6 and thiamine can be measured in blood. If you have nerve symptoms, mention any B6 supplements, as high blood B6 helps confirm toxicity.

Before you blame yourself

Many people take a B complex because they feel exhausted and stressed, and feel let down when nothing changes. That is not a sign that you are doing something wrong. Most tiredness comes from sleep, stress, workload, iron or B12 deficiency, thyroid problems, depression or other medical causes, and a supplement cannot fix those on its own.

If you developed tingling after taking B6 products, it is not your fault either. These supplements were sold as harmless, and many labels still do not make the risk clear.

When to see a doctor

See a doctor if:

• you have numbness, tingling, burning or balance problems, especially if you take B6, metformin or acid-reducing medicines, or follow a vegan diet;

• you feel tired, breathless or pale for more than a few weeks;

• you have a sore tongue, mouth ulcers or memory changes;

• you are over 50, vegan or have a gut condition and have never had B12 checked;

• you are pregnant with severe nausea and vomiting;

• you drink heavily or have had weight-loss surgery.

Go to an emergency room for new confusion, unsteady walking, or abnormal eye movements or double vision, especially with heavy alcohol use, severe vomiting in pregnancy or after weight-loss surgery. These can be signs of Wernicke encephalopathy, a medical emergency caused by severe thiamine deficiency (11).

How to bring this up with your doctor

What to ask for, by name. "Could we check vitamin B12, folate and a full blood count?" If you have nerve symptoms: "Could my B6 supplements be causing this? Could we check my B6 level?"

What to bring. Every supplement bottle you take, or photos of the labels, with the B6, B12 and folic acid amounts per dose, how many doses you take, and all medicines, especially metformin, omeprazole or similar.

What to say, out loud. "I've been taking [B complex / magnesium with B6 / energy drinks] for [time]. Recently I've noticed [tingling in my feet / tiredness / poor balance]. Could these be connected?"

If you're told your B12 is "normal". Borderline levels can still matter with symptoms. Ask: "Is my result at the low end, and would a methylmalonic acid test help?"

How long until you notice a difference? Most supplements take weeks, not days. See how long supplements take to work, and how to tell if one is working.

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How Welltory helps — and what it cannot do

The limits first. Welltory is a general wellness product, not a medical device. It cannot measure B vitamins, detect deficiency or nerve damage, or tell you whether a supplement is working.

What it can do is help you see whether a change in routine coincides with changes in how you sleep and recover.

Tag supplements and symptoms. On iOS with an Apple Watch or Oura, when Welltory marks a stress or rest episode on the Today screen and asks "What happened?", tap, type or talk: "started B12", "stopped B6", "tingling feet", "low energy". Over weeks, My Patterns shows which tags tend to appear with stress and recovery; some sections need a paid plan.

Sleep and morning energy. Sleep Analysis uses Apple Watch or Oura data on iOS and on Android works with Samsung Health, or with Fitbit and Garmin Connect through Health Connect (Sleep Analysis for Android). On the iOS Today screen (with Apple Watch or Oura), Battery starts each morning from your resting heart rate on waking and your sleep (Today screen). HRV measurements show how your body handles stress over time.

A record for your doctor. From the web app you can export a CSV (Dashboard → choose a chart → Export) (export guide) to bring alongside your blood test results and supplement list. Trends are associations to discuss with your doctor, not proof of deficiency or that a supplement worked.

How we made it

We based this article on NIH Office of Dietary Supplements fact sheets on vitamins B12 and B6, a 2019 systematic review and meta-analysis of B vitamins for stress, anxiety and mood, the 2023 European Food Safety Authority opinion on the upper limit for vitamin B6, the Australian Therapeutic Goods Administration's 2025 safety update on vitamin B6, a 2026 overview of international regulatory action on B6, a Cochrane review comparing oral and injected B12, the NIH fact sheet on riboflavin, the US Food and Drug Administration and American Thyroid Association on biotin and lab tests, and MedlinePlus on Wernicke encephalopathy. Search questions came from what people in the United States most often ask about B complex, B12 and B6. For the product section, we checked every function against the Welltory Help Center on October 21, 2026.

Made with AI tools, then edited and fact-checked by the Welltory team. See our Editorial & AI policy.

Jane Smorodnikova, co-founder of Welltory, built the methodology behind how we read physiological data.

Written by Tatsiana Yashyna.

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