Quick answer

A B complex combines B vitamins your body uses to release energy from food and to make DNA and red blood cells. Adults need small amounts, from 2.4 mcg of vitamin B12 to 16 mg of niacin a day, and most people get enough from food. Extra amounts have not shown added benefit.^1,2,3

Key facts

There are eight B vitamins, and B complex products differ in which ones they include and in how much.^1,3
People over 50 are advised to get most of their vitamin B12 from fortified foods or supplements.^1,4
For adults, upper limits apply to niacin (35 mg) and folic acid (1,000 mcg) from supplements and fortified foods, and to vitamin B6 (100 mg).⁴
Vitamin B12 does not add energy or endurance in people who already get enough.¹
B complex products can contain biotin, which can distort some blood tests.^5,6

What a B complex is

A B complex supplement combines several B vitamins in one product. The same vitamins are also sold one at a time and appear in most multivitamins.^5,7,8

There are eight B vitamins: thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid, vitamin B6, biotin (B7), folate (B9) and vitamin B12. All of them dissolve in water.^2,3,6,9,10

The eight B vitamins at a glance^{4,5,7,8,9,10,11,12,13}
Vitamin	Main job	Adults need per day
Thiamin (B1)	Helper for enzymes that use sugars, amino acids and fats	1.1 to 1.2 mg
Riboflavin (B2)	Part of two coenzymes used to produce energy	1.1 to 1.3 mg
Niacin (B3)	Forms NAD, which more than 400 enzymes use	14 to 16 mg NE
Pantothenic acid	Part of coenzyme A, used to make and break down fats	5 mg
Vitamin B6	More than 100 enzyme reactions, mostly with protein	1.3 to 1.7 mg
Biotin (B7)	Helper for five enzymes that use fats, sugars and amino acids	30 mcg
Folate (B9)	Making DNA and dividing cells	400 mcg DFE
Vitamin B12	Nerves, red blood cells and DNA	2.4 mcg

Products differ in which B vitamins they include and how much of each they contain, so the Supplement Facts panel is the only way to know what a given B complex supplies.^1,7

What the evidence shows

Each claim below carries a grade and the amount behind it. All three are basic nutrient roles rather than results from supplement trials, so they describe what getting enough does, not what extra adds.³

Provides B vitamins that contribute to normal energy-yielding metabolism*^{9,11,12,13,14}

Moderate evidence

Thiamin, riboflavin, niacin, pantothenic acid, vitamin B6, vitamin B12 and biotin are needed by the enzymes that release energy from food; niacin alone is part of a coenzyme used by more than 400 enzymes. 'Contributes to normal energy-yielding metabolism' is the wording European regulators permit for each of these vitamins. It does not mean extra B vitamins give more energy to someone who already gets enough.

Amount studied: Recommended daily amounts of each B vitamin, from food and supplements together

Provides folate and vitamin B12, which the body needs to make DNA and normal red blood cells*^1,3,7,10,15

Moderate evidence

A long-established role of both vitamins rather than a finding from supplement trials. NIH describes vitamin B12 as required for healthy red blood cell formation and DNA synthesis, and folate as needed to make DNA and for cells to divide; when either runs short, red blood cells form abnormally. The Institute of Medicine found no observable health benefit from B vitamin intakes beyond those that avoid the signs of running short.

Amount studied: Recommended amounts for adults: 400 mcg DFE of folate and 2.4 mcg of vitamin B12 a day

Provides vitamin B12, which the nervous system needs to develop and work normally*^1,7

Moderate evidence

A long-established role rather than a finding from supplement trials. NIH describes vitamin B12 as required for the development, myelination and function of the central nervous system, and running short can cause numbness and tingling in the hands and feet. In trials of older adults, vitamin B12 taken alone or with other B vitamins did not change scores on thinking and memory tests.

Amount studied: Recommended amount for adults: 2.4 mcg of vitamin B12 a day

Vitamin B12 is often sold for energy and endurance, but it does not provide those benefits in people who already get enough.^1,7

Who is more likely to fall short

Most people in the United States get enough of each B vitamin from food. About 6% fall short of thiamin and under 6% of riboflavin, and about 1% of adults fall short of niacin.^9,11,12

Because many older adults absorb less of the vitamin B12 in food, people over 50 are advised to get most of their B12 from fortified foods or supplements, whose B12 is easier to absorb.^1,4

People who eat no animal foods get no natural vitamin B12 and need fortified foods or supplements. Vegans and people who eat little dairy are also more likely to fall short of riboflavin.^7,16

NIH advises all women and teen girls who could become pregnant to get 400 mcg of folic acid a day from supplements, fortified foods or both, on top of the folate in a varied diet.^4,15

Long-term heavy drinking also makes running low more likely, for thiamin, folate and vitamin B6 among others, and some medicines lower B12 or folate, as the safety section below explains.^15,17,18

How much is in a B complex

B-complex supplements generally contain 50 to 500 mcg of vitamin B12, compared with 5 to 25 mcg in a typical multivitamin and 500 to 1,000 mcg in products with B12 alone.⁷

Supplements for adults commonly contain 400 to 800 mcg of folic acid, which counts as 680 to 1,360 mcg DFE.¹⁰

Products like these supply many times the daily need for some B vitamins. Check the panel against the upper limits in the safety section, especially if you also take a multivitamin, because the limits count every product together.^4,7

Food first

No single food is rich in every B vitamin, but a mix of meat, fish, eggs, dairy, legumes, leafy greens and whole or enriched grains covers them. In the United States, enriched grains also carry added folic acid, thiamin, riboflavin and niacin.^1,15,17

Plant foods have no vitamin B12 unless it is added. Fortified breakfast cereals and fortified nutritional yeasts are readily available sources, and the body absorbs their B12 well.^1,7

What's in ours

What’s in ours

Men's Multi: Vitamin B1, 7 mg per serving, from the label

The Men's Multi panel lists all eight B vitamins. The card shows the first of them, and the product page shows every amount.

Side effects, medicines, and who should ask first

For adults, the upper limits are 35 mg a day of niacin and 1,000 mcg a day of folic acid from supplements and fortified foods, and 100 mg a day of vitamin B6 from all sources. No upper limit is set for thiamin, riboflavin, pantothenic acid, biotin or vitamin B12, for lack of data, though caution may still be warranted above recommended amounts. In 2023 Europe's food safety authority set a lower limit for vitamin B6 of 12 mg a day.^4,8,10,12

Nicotinic acid, one form of niacin, typically causes flushing at 30 to 50 mg or more: the skin of the face, arms and chest turns red and can burn, tingle and itch. It can start within 30 minutes and usually passes. It is unpleasant rather than harmful, but it can come with headache, rash, dizziness or a drop in blood pressure.^2,12

Taking 1 to 6 g of vitamin B6 a day for 12 to 40 months can cause severe nerve damage with loss of control of body movements, which usually stops when the supplement is stopped. Too much B6 can also cause painful skin patches, sensitivity to sunlight, nausea and heartburn.^8,18

Large amounts of folic acid can correct the anemia caused by a vitamin B12 deficiency while the nerve damage continues, which can delay the diagnosis, and may make the deficiency worse. This is the basis of the upper limit for folic acid.^10,15

Ask your pharmacist or doctor first

B complex supplements can contain biotin. The levothyroxine label says biotin interferes with thyroid hormone tests built on biotin and streptavidin, which may give wrong results, and tells patients to stop biotin and any biotin-containing supplement for a time before thyroid function testing.^5,19

On the medicine's label

Ask your pharmacist or doctor first

The methotrexate label says products containing folic acid may make methotrexate less effective when it is used for cancer, and that patients should take them only when their healthcare provider directs. For other uses, the label tells prescribers to give folic acid or folinic acid to lower the chance of side effects.^10,20

On the medicine's label

Ask your pharmacist or doctor first

Anticonvulsants such as phenytoin, carbamazepine and valproate can lower folate and vitamin B6 levels, and long-term use has been linked to lower biotin. Folate supplements might lower blood levels of these medicines, and 200 mg a day of vitamin B6 lowered blood levels of phenytoin and phenobarbital.^5,8,10

Reported in studies

Your doctor may want to check on you

Metformin may lower vitamin B12 levels, possibly by reducing its absorption. The metformin label recommends measuring vitamin B12 every 2 to 3 years in people who take it.^7,21

On the medicine's label

Your doctor may want to check on you

Daily use of acid-reducing medicines such as omeprazole over a long time, for example more than 3 years, can reduce how much vitamin B12 the body absorbs from food. The omeprazole label notes rare reports of B12 deficiency.^7,22

On the medicine's label

Ask first if you take methotrexate, an anticonvulsant, metformin, a medicine that lowers stomach acid, or levothyroxine
Ask first if you are pregnant, could become pregnant or are breastfeeding
See a doctor about numbness or tingling in your hands or feet rather than treating it yourself, since it can be a sign of low vitamin B12¹
Tell your doctor and the lab what you take before blood tests⁶

Questions people ask

Does B complex give you energy?

Not if you already get enough. B vitamins help the body release energy from food, but NIH says vitamin B12 does not raise energy or endurance in people who get enough, and the Institute of Medicine found no benefit from intakes above need. Tiredness that lasts is a reason to see a doctor.^1,3

What does B complex do for men?

The same things it does for women. Men need slightly more thiamin (1.2 mg), riboflavin (1.3 mg) and niacin (16 mg NE) than women, and after 50 they need 1.7 mg of vitamin B6 a day.^2,16,17,18

Is B complex good for hair?

No B vitamin has been shown to change hair in people who get enough of it. Biotin, the one most often sold for hair, has evidence that NIH describes as limited to case reports and small studies.⁵

Why does B complex turn urine bright yellow?

Riboflavin is yellow, and the body passes what it does not absorb or use in urine. NIH describes discolored urine as a minimal side effect.⁹

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See the Full Measure line Men's Multi

Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.