Do Multivitamins Really Work?

What are multivitamins? Why do people take them? 

Multivitamins are over-the-counter products available for purchase in most grocery stores and pharmacies. They may contain vitamins, minerals, and or other herbal supplement ingredients.

People often decide to take a multivitamin because they are not getting enough of these ingredients from their regular diet or to maintain good health. Some restrictive diets, like vegetarianism, can limit the amount of vitamin B12, iron, and calcium that a person normally gets from food. Taking a multivitamin would therefore help replenish those deficiencies while allowing the person to healthily maintain their diet. Pregnant patients often take multivitamins containing folic acid as it has been shown to support the healthy development of the growing baby.

Do multivitamins work?

Multivitamins come in a variety of forms, including tablets, gummies, and liquids. Different companies may also vary the amounts of each ingredient contained in a given product. Because every product is different, it is difficult for scientists to confirm the efficacy of multivitamins. However, multivitamins are generally considered helpful in certain circumstances.

Multivitamins can help people who do not otherwise get sufficient vitamins and nutrients in their regular diet. Some vitamins are thought to help specific patients. For example, vitamin E and beta carotene have been thought to boost eye health and prevent vision loss in patients with cataracts or age-related macular degeneration. Various diseases such as lung disease, heart disease, and psychiatric disorders have all been examined to see if a multivitamin could improve patient care. Most studies have shown no significant improvements in these patients. 

What are the side effects of multivitamins?

For most people, multivitamins typically have only mild side effects. The most common side effects associated with multivitamins tend to be nausea and upset stomach. People are often concerned that multivitamins may cause weight gain, but there are currently no studies confirming that multivitamins influence weight gain or weight loss in most people. Patients who are malnourished and do not get enough vitamins regularly may see an increase in weight when they correct their diet and get the daily recommended requirements for each vitamin and mineral.

Can you overdose on multivitamins?

Generally, multivitamins are unlikely to harm your health when taken as directed. Experts advise that people should not take more than the daily recommended upper dose limit of a given vitamin. Many vitamins are well tolerated, but some can lead to unpleasant or harmful effects at high doses. 

Iron is a mineral that is often found in multivitamins. Iron-containing multivitamins can be extremely toxic in children and adults when large doses are consumed. Prenatal vitamins usually contain higher amounts of iron than a regular adult or children’s multivitamin and can be especially dangerous. Prenatal vitamins are often found in households with young children because they are either leftover from the pregnancy or are from a current pregnancy of a sibling, placing these children at higher risk of accidental overdose from iron. Early signs of iron poisoning include abdominal pain, vomiting, and diarrhea. Large doses of iron can cause bleeding, shock, damage to the stomach and intestines, low blood pressure, liver damage, and death. It is important to keep iron-containing vitamins out of reach of small children.

Vitamin C is found in many multivitamins and food products. While it is usually tolerated very well, it has also been associated with causing kidney stones in rare cases. High doses of vitamin C can also cause diarrhea.

B vitamins are another commonly taken category of vitamins. There are several vitamins in the B family, and most of them cause few side effects. However, vitamin B-3, also known as niacin, can lead to red, flushed skin and an upset stomach. Niacin can cause liver damage if an extremely large amount is taken. 

Can multivitamins be poisonous?

For most healthy people, multivitamins are unlikely to be harmful and may assist in replenishing missing vitamins and minerals. However, people with certain health conditions or who take certain medications should avoid some types of multivitamins. These individual patients should discuss whether taking specific products and vitamins are appropriate with their healthcare professionals. Some smokers are asked to avoid taking multivitamins that contain vitamin A because one study suggests this vitamin may further increase the risk for lung cancer in smokers.

What should I do if I take too many multivitamins or take them by accident? 

If you believe you or someone else has taken too many multivitamins, it is important to remain calm. Do not force yourself or the person to try and throw up since many multivitamins only cause mild side effects with extra doses. 

Help from experts is available through the webPOISONCONTROL online tool and by phone at 1-800-222-1222. Poison Control’s expert guidance is always free, confidential, and available 24 hours a day. 

Terri Shamis, Pharm.D, CSPI
Pharmacist and Certified Specialist in Poison Information  

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