Can multivitamins have side effects?

Multivitamins are some of the most used supplements on the market. They are convenient, help to plug any nutrient gaps in your diet, and provide another defence against the unwellness that can come along with deficiencies in the body. Although they are no replacement for a healthy balanced diet with a wide nutritional profile, multivitamins can help to give you the peace of mind that comes with knowing you are actively doing something positive for your nutritional health each day. 

However, with so many different vitamin and mineral combinations and so many different dosage recommendations, you might find yourself staring at a wall of bottles and wondering if some are safer for you than others or if there might be side effects to using them. 

When you begin taking any new supplement, there may well be a period of adjustment for your body which causes some side effects, and multivitamins are no exception. This article will look at some of the common, and less common, side effects of taking a multivitamin and if there’s anything to look out for which could indicate a wider issue. 

Side effects in adults: 

When you first begin taking a multivitamin, you might notice some small stomach issues such as constipation, diarrhoea and nausea. These will usually dissipate as your body becomes accustomed to receiving nutrients in this way (Kamangar and Emadi, 2012).

Less common side effects include nosebleeds, insomnia and gout. This is often related to the way in which the nutrients in multivitamins can interact with the nutritional content of your diet. The majority of nutrients have a scientifically calculated upper level, which is how much of any one nutrient can be safely consumed in a day (Biesalski and Tinz, 2017).

This is different to the Recommended Daily Intake, which is likely to be much smaller than the upper level. Scientists believe that the upper level is where a nutrient begins to display toxicity in the body. For some vitamins, such as B12, no upper level has been set due to its low toxicity and the fact that it is water soluble, so any ‘extra’ that your body isn’t using will simply be excreted during the day (Ronis, Pedersen and Watt, 2018).

Combining multivitamins with other supplements or eating a lot of foods fortified with extra nutrients may also pose an increased risk of developing side effects due to cumulatively exceeding the upper levels of various vitamins and minerals. 

In very rare cases, some people have experienced anaphylactic reactions to multivitamins which can include hives, swelling of the face, tongue and throat, and difficulty breathing. In these instances, emergency help must be sought immediately. Taking the multivitamins with you will help identify what caused the allergy response so that it can be avoided in the future. 

Side effects in children:

Children can also experience side effects in much the same way as adults, although their upper level for a lot of nutrients is lower than that of an adult. For children, taking a multivitamin, even one designed especially for younger people, can put them over the upper level threshold, which could lead to nutrient overdose which, in some cases, has unfortunately been fatal. 

Multivitamins that contain iron, for example, may prove to be an unwise choice for younger children who do not need extra iron in their diet. In fact, overdosing on iron is one of the lead causes of poisoning in children (Elliott, 2019).

As with any kind of supplement, be sure to seek the advice of a healthcare professional before starting your child with multivitamins, as they may be getting everything they need from their diet alone.

Side effects of large doses:

There is something of a consensus that having more of something that’s good for you will increase the benefits it holds exponentially. 

With vitamins and minerals, this isn’t the case. Regularly exceeding the recommended daily intake for certain nutrients can do more harm than good. In the case of certain fat-soluble vitamins, which the body can store over time, regularly taking larger doses can cause a toxic build up which can have a huge impact on your health (Ronis, Pedersen and Watt, 2018). 

It’s good to remember that when you’re choosing your multivitamin, it is there to fill any gaps in your nutrition, not provide 100% of what you need in a day. There are certain key nutrients which the body needs to function and must be ingested or created every day, which can have a negative effect on other areas of our health if taken to excess. 

Let’s look at some of the side effects potentially posed by those nutrients.


Side effects of certain nutrients in large doses:

The vitamins and minerals within a typical multivitamin tend to fall into three categories; water-soluble vitamin, fat-soluble vitamin, and mineral. Each of these is handled in a different way by the body and can cause different side effects. Those side effects are also determined by which of the nutrients is causing them, and whether they are stored in the body. 

Fat-soluble vitamins, such as Vitamins A and E dissolve in fat and accumulate in the body, meaning that they can reach toxic levels if taken in excess over long periods. 

  • Excessive consumption of Vitamin A can cause birth defects and liver damage, as well as weakening your bone structure, and increasing the risk of lung cancer in smokers (Ronis, Pedersen and Watt, 2018)
  • Taking too much Vitamin E may result in blurred vision, feelings of weakness and fatigue, and fertility problems. 

Minerals, such as iron, zinc, and copper, can also accumulate in the body and may also cause potentially harmful side effects (Kamangar and Emadi, 2012). 

  • Taking high amounts of copper, magnesium, iron and zinc, for example, has been shown to cause stomach problems including pain, vomiting, nausea and constipation. 
  • Too much iron can also cause liver damage. 
  • An excessively high mineral intake can also prevent your body from absorbing other nutrients, causing deficiencies in other areas. 

Water-soluble vitamins, such as B12 and Vitamin C, are usually safe in larger quantities as they aren’t stored in the body and can be excreted through urine as they dissolve. They are also unlikely to cause major side effects if taken in excess. However, this doesn’t mean that excessively high doses won’t cause some side effects.

  • Take Vitamin C, for example. Continuous large doses of Vitamin C may cause stomach cramps, migraines and vomiting (Muhammad Abdullah, Jamil and Attia, 2019).
  • Niacin, also known as Vitamin B3, can cause liver damage if taken in high doses over long periods of time. It can also result in Niacin flush, which causes an irritation to the skin (National Institutes of Health, 2017)
  • Whilst you’d need to take B6 at 10 times the upper level frequently to start seeing the side effects, excessive dosing can lead to skin lesions, heart problems, neurological damage and photosensitivity. 
  • Folic acid, otherwise known as Vitamin B9, may also present certain side effects at really high doses, including masking the symptoms of B12 deficiencies, which can be really serious and cause permanent neurological and nerve damage.

Some multivitamins and other supplements have also been shown to contain high levels of contaminants, such as heavy metals and pesticides, which can also build to toxic levels in the body and cause both physical and neurological damage (Costa et al., 2019).

All of this isn’t designed to scare you, but encourage you to find a multivitamin which will safely suit your needs. Most of the side effects listed here occur when excessive consumption of certain nutrients happens over time. Forgetting that you’ve taken your multivitamin first thing in the morning and taking another is not going to be harmful. 

When looking for a multivitamin, it is wise to choose one which does not contain 100% of the Recommended Daily Intake for each nutrient. This is to ensure that you multinutrient can fill any nutrient gaps without creating an excessive intake which may cause health problems over time. 

Vivo Life’s Multinutrient and Mineral Supplement has been formulated with vegans in mind, making it suitable for diets which contain fortified foods, and providing a functional dose of 11 key vitamins and minerals without exceeding upper levels. More than that, the multivitamins are third party tested for contaminants, including heavy metals so that you can use them with confidence. 


Kamangar, F. and Emadi, A. (2012). Vitamin and mineral supplements: do we really need them? International journal of preventive medicine, [online] 3(3), pp.221–6. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3309636/. 

Biesalski, H.K. and Tinz, J. (2017). Multivitamin/mineral supplements: Rationale and safety. Nutrition, [online] 36, pp.60–66. doi:10.1016/j.nut.2016.06.003.

Elliott, C. (2019). Assessing Vitamins, Minerals and Supplements Marketed to Children in Canada. International Journal of Environmental Research and Public Health, 16(22), p.4326. doi:10.3390/ijerph16224326.

Muhammad Abdullah, Jamil, R.T. and Attia, F.N. (2019). Vitamin C (Ascorbic Acid). [online] Nih.gov. Available at: https://www.ncbi.nlm.nih.gov/books/NBK499877/.

Ronis, M.J.J., Pedersen, K.B. and Watt, J. (2018). Adverse Effects of Nutraceuticals and Dietary Supplements. Annual Review of Pharmacology and Toxicology, [online] 58(1), pp.583–601. doi:10.1146/annurev-pharmtox-010617-052844.

Costa, J.G., Vidovic, B., Saraiva, N., do Céu Costa, M., Del Favero, G., Marko, D., Oliveira, N.G. and Fernandes, A.S. (2019). Contaminants: a dark side of food supplements? Free Radical Research, 53(sup1), pp.1113–1135. doi:10.1080/10715762.2019.1636045.

National Institutes of Health (2017). Office of Dietary Supplements - Niacin. [online] Nih.gov. Available at: https://ods.od.nih.gov/factsheets/Niacin-HealthProfessional/.