Multivitamin

Are multivitamins safe?

A basic once-a-day multivitamin is one of the lower-risk supplements you can take. It supplies roughly the daily values of 20 or so vitamins and minerals, well under the upper limits, and the large trials gave them to tens of thousands of people for years without safety signals. About one in three US adults takes one, according to the NIH Office of Dietary Supplements (ODS).

The catches are specific. Adult products with iron can kill a toddler who swallows a handful. Retinol is a problem in pregnancy, beta-carotene is a problem for smokers, and people who stack a multi with single vitamins and fortified foods can go over limits. And the benefit for well-fed adults is small or absent.

Do multivitamins actually work?

Mostly not for the reasons people buy them. The three biggest studies point the same way.

• Physicians' Health Study II (JAMA, 2012) gave 14,641 US male doctors aged 50 and over a daily Centrum Silver or a placebo for a median 11.2 years. Total cancer fell by 8% (hazard ratio 0.92), but there was no effect on any single cancer, on cancer deaths or on heart attacks and strokes.
• COSMOS (American Journal of Clinical Nutrition, 2022) randomised 21,442 older US adults for a median 3.6 years. Total invasive cancer, cardiovascular events and deaths were no different from placebo; lung cancer was lower, a secondary finding.
• A 2024 NIH-led cohort in JAMA Network Open followed 390,124 healthy US adults for up to 27 years. Daily users had no lower risk of death; in the first half of follow-up their risk was even slightly higher (hazard ratio 1.04), and the authors concluded there was no mortality benefit.

The one consistent positive is memory in older adults. Three COSMOS sub-studies with more than 5,000 participants found a small benefit on global cognition and episodic memory, which the authors equated to about two years less cognitive ageing. The US Preventive Services Task Force concluded in 2022 that there is not enough evidence to judge the balance of benefit and harm for preventing heart disease or cancer.

Multivitamins make more sense for people with poor diets, strict vegans, people after weight-loss surgery, and pregnancy, where a prenatal formula is standard advice.

Iron and children

This is the most serious risk, and it has nothing to do with the person the pills were bought for. Iron tablets look like sweets, and a few adult tablets can seriously poison a small child. Iron damages the gut and liver, and the child can seem to recover before getting much worse.

In 1997 the FDA made a boxed warningBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary compulsory on every solid iron-containing supplement: "Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6." A study of US poison centre data (Archives of Pediatrics & Adolescent Medicine, 2005) found deaths from iron poisoning in children under 6 fell from 29 in the ten years before the rule to 1 in the five years after. Store any multi with iron, including prenatal vitamins, out of reach and in the original child-resistant container. More on iron itself is on our iron page.

Vitamin A, beta-carotene and pregnancy

Some general and "high-potency" multis contain preformed vitamin A (retinol). Too much early in pregnancy can cause birth defects; the upper limit for pregnant women is 3,000 mcg a day, from food and supplements combined. Prenatal products generally avoid retinol, which is one reason to use one. See our vitamin A page for the details.

Smokers and former smokers should avoid multis with large amounts of beta-carotene. In two big trials, beta-carotene supplements raised lung cancer in smokers by 18% and 28%, and NIH ODS advises smokers to avoid such products.

Interactions with medicines

NIH ODS says multivitamins at recommended amounts do not usually interact with medicines, with one important exception: vitamin K and warfarin. Warfarin doses are set around your usual vitamin K intake, so starting or stopping a multi can shift your INR.

The minerals also matter for timing. Iron, calcium, magnesium and zinc bind some antibiotics, such as ciprofloxacin and the tetracyclines, and reduce absorption of levothyroxine, so these are usually taken hours apart. If you take any regular medicine, talk to your doctor or pharmacist about timing.

Is the label accurate?

Not always. In August 2026 Consumer Reports tested 17 popular prenatal multivitamins: only 2 were within US Pharmacopeia (USP) tolerances for every nutrient measured, and 32% of the 126 nutrient results fell outside them. Gummies varied most; half of the eight gummy products had less folate than labelled, and one delivered 28% of its stated folic acid. None exceeded the safety limits for heavy metals used in the test. ConsumerLab's 2023 review failed 7 of 27 multis for nutrient amounts far off the label, including gummies with nearly double their folate.

Recalls are mostly about manufacturing. In May 2026 a US maker recalled a range of liposomal liquid multivitamin drops, including children's drops, for good manufacturing practice failures that could allow bacteria including Clostridium botulinum (Class II, FDA enforcement records).

How to pick and use one

1. Choose a basic formula with most nutrients at or near 100% of the daily value, not a "mega" or "high-potency" product.
2. Match it to your life stage: prenatal in pregnancy, a 50+ formula (usually little or no iron) for older men and post-menopausal women.
3. Look for the USP VerifiedThird-party testingTesting of a supplement by an independent lab to check that it contains what the label says and is free of set contaminants.More in the glossary mark or another third-party seal, and prefer tablets or capsules over gummies if accuracy matters to you.
4. Add up everything else you take, especially vitamin A, niacin, zinc and iron.
5. Lock it away from children if it contains iron.

How we scored it

Dose safety (85) and organ toxicity (82) are strong because basic multis sit well under upper limits; the main deduction is acute iron poisoning in children. Interactions (78) reflect warfarin and mineral binding. Product quality (70) is the weakest factor, after recent tests found many prenatal and gummy products off-label. Regulatory actions (80) reflect the mandatory iron warning and recent recalls, with no bans.