Can You Take Multiple Supplements at Once?

Quick answer

Many adults do: 13.8% of US adults used four or more supplements in 2017-2018. NIH says side effects are most likely with high doses, with many different supplements, or when supplements replace medicines. Check that amounts do not overlap across products, that minerals do not compete, and that nothing interacts with your medicines.^1,2

Key facts

In 2017-2018, 57.6% of US adults used a supplement in the past 30 days and 13.8% used four or more.¹
NIH says side effects are most likely if you take high doses, take supplements instead of prescribed medicines, or take many different supplements.²
Upper limits for vitamin D, zinc and several other nutrients count intake from all sources, including food, drinks and supplements; magnesium's limit counts supplements and medicines only.^3,4,5
Iron at 25 mg or more taken at the same time as zinc can lower zinc absorption, and experts suggest taking calcium and iron at different times.^6,7
In a USDA-led analysis of adult multivitamins, measured amounts exceeded the label for every nutrient except thiamin, by 1.5% to 13% for many and about 25% for selenium and iodine.⁸
FDA lists combining supplements and mixing them with medicines among the situations where problems occur.⁹

How common is it to take several supplements?

In the 2017-2018 national survey, 57.6% of US adults 20 and older used at least one dietary supplement in the past 30 days. The same survey counted how many each person used.¹

US adults 20 and older, by number of supplements used in the past 30 days, 2017-2018¹
Supplements used	Share of adults
None	42.4%
One	22.5%
Two	13.8%
Three	7.5%
Four or more	13.8%

Can you take all supplements at once, or should you spread them out?

The sources have no rule for supplements as a group. They describe specific pairs that compete for absorption and specific products that interact with medicines, and they say nothing against taking compatible products together. That is not a clearance: the sources checked do not address most pairs, so a pharmacist is the person to ask about your own list.^2,6,7,9

Spreading doses out has reasons of its own. The share of calcium absorbed falls as a single amount rises above 500 mg, vitamin B12 and vitamin C show the same pattern, and our timing guide has the chart.^10,11,12

Do the amounts add up across products?

Yes, and the sum is easy to miss. Upper limits are set for total intake. For vitamins D and C, iron and zinc, NIH says the upper limit includes food, drinks and supplements; for magnesium it counts supplements and medicines only. Fortified foods count too: an analysis of national survey data found that eating more voluntarily fortified foods went with a greater chance of calcium and iron intakes above the upper limit in some adult groups.^{3,4,5,13,14,15}

The label may also understate a product. Makers add extra to cover losses over shelf life, and in a USDA analysis of adult multivitamins, measured amounts exceeded labeled amounts for every nutrient except thiamin, by 1.5% to 13% for many and about 25% for selenium and iodine. NIH adds that people who take multivitamins, other supplements and fortified foods might exceed an upper limit.^8,16

Example only: adding two products' labels (hypothetical amounts)^3,4,5
Nutrient	Product A	Product B	Total	Adult upper limit
Vitamin D	25 mcg	50 mcg	75 mcg	100 mcg (4,000 IU), all sources
Zinc	15 mg	15 mg	30 mg	40 mg, all sources
Magnesium	200 mg	200 mg	400 mg	350 mg, supplements and medicines only

The labeled amounts in the table are made up to show the arithmetic. Add up the amount per serving across everything you take, and compare the total with the upper limit for your age; our upper limit checker does the sum.³

Which supplements compete for absorption?

Iron and zinc: supplements with 25 mg of iron or more taken at the same time as zinc can reduce zinc absorption and blood zinc.⁶
Calcium and iron: calcium might interfere with iron absorption, although this has not been definitively established, so experts suggest taking individual calcium and iron supplements at different times of the day.⁷
Zinc and copper: high zinc intakes can interfere with copper absorption, and excessive zinc supplement use can lead to copper deficiency.¹⁷

Eating foods that contain vitamin C at the same meal as plant sources of iron helps the body absorb more of that iron.^18,19

In the same study, taking the selenite mixed with 1 g of vitamin C on an empty stomach cut the selenium absorbed almost to zero.²⁰

What should you ask a pharmacist before taking several supplements together?

FDA says some supplements can interact with medicines, interfere with lab tests, or have dangerous effects during surgery. NIH gives examples: vitamin K can reduce how well warfarin prevents clotting, and St. John's wort can speed the breakdown of many medicines. NIH also says to keep a complete record of every supplement and medicine, with the dose and how often you take each, and to share it with your health care providers.^2,9

Which of my products contain the same nutrient, and what is the total for the day?
Do any of my supplements interfere with a medicine I take, or with a blood test I have coming up?
Should any two be taken at different times of day?
Is a pill I find hard to swallow available in a smaller form? NCCIH notes that older adults have had swallowing problems from large vitamin pills.²¹

Questions people ask

Can you take multiple vitamins at once?

Many people do, and NIH says problems are likelier with high doses or many different supplements. The checks are overlapping amounts, pairs that compete such as iron and zinc, and medicine interactions.^2,6

Can you take all supplements at once?

The sources give no rule for supplements as a group. Calcium is absorbed best at 500 mg or less at a time, and iron at 25 mg or more can lower zinc absorption, so spacing products out is one way to handle both.^6,10

Should you take multiple supplements at once?

That depends on your products, doses and medicines. Ask a pharmacist, who can check your whole list against upper limits and interactions.^2,9

Can you take two pills at once?

The sources name specific pairs to keep apart and say nothing against most combinations, which is not a clearance. Add the amounts of any shared nutrient, compare the total with its upper limit, and ask a pharmacist about medicines.^3,4

Can you take many supplements at once?

In 2017-2018, 13.8% of US adults used four or more. NIH says side effects are most likely with many different supplements, so keep a written record and share it with your providers.^1,2

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Sources

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