Supplement Stack Checker: Upper Limits

Quick answer

Pick two or more of our products and the checker adds up what their labels provide in a day. It compares the totals with six tracked amounts: vitamin D 100 mcg, magnesium from supplements 350 mg, zinc 40 mg, vitamin B6 100 mg, niacin 35 mg, and a full 5 g dose of creatine.^1,2,3,4,5,6

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Pick at least two.

Key facts

The adult vitamin D limit is 100 mcg (4,000 IU) a day from all sources, food included.¹
The magnesium limit of 350 mg a day applies to supplements and medicines only, not to magnesium in food.²
The adult zinc limit is 40 mg a day from all sources, and it is set to protect copper status.³
The niacin limit is 35 mg a day from supplements and medicines, set at the level linked to flushing.⁵
The US vitamin B6 limit is 100 mg a day, while the European Food Safety Authority set a lower adult limit of 12 mg in 2023.^4,7
No upper limit is set for creatine, and the trials used 3 to 5 g a day after a loading phase.^6,8

What the checker does

Choose two or more of our products. For each one, the checker reads the amounts on its Supplement Facts panel and multiplies them by the servings per day the label directs. It then adds up each tracked nutrient across the products you picked.

A note appears only when at least two of the picked products carry the same nutrient and their total reaches its limit. For vitamin D and magnesium, a second kind of note appears when the total comes within 15 percent of the limit.

The checker also shows a short note for a few pairs of our products that overlap for another reason, such as two products with the same main ingredient, or two that can each cause drowsiness.

The checker adds up our products only. It does not count food, other supplements or medicines, so a result with no notes is not a clearance. The vitamin D and zinc limits count every source, food included.^1,3

What an upper limit is

An upper limit, formally the Tolerable Upper Intake Level, is the maximum daily intake unlikely to cause adverse health effects. It is a ceiling and not a target, and the amount you are advised to get is often lower.⁹

Limits differ in what they count. Some cover every source of the nutrient, food included. Others cover supplements and medicines only, which is why the 350 mg magnesium limit can sit below the amount men are advised to get in total, 400 to 420 mg.^2,10

The six amounts the checker tracks^1,2,3,4,5,6
Nutrient	Amount used	What it counts	When the checker speaks up
Vitamin D	100 mcg (4,000 IU) a day	All sources, food included	At the limit, and from within 15 percent of it
Magnesium	350 mg a day	Supplements and medicines only	At the limit, and from within 15 percent of it
Zinc	40 mg a day	All sources	At the limit
Vitamin B6	100 mg a day	Food and supplements together (US limit)	At the limit
Niacin	35 mg a day	Supplements and medicines	At the limit
Creatine	One full 5 g dose	No upper limit is set	When two products add up to more than one 5 g dose

The limits in full

The upper limit for adults and children aged 9 and over is 100 mcg (4,000 IU) a day from all sources, including during pregnancy and breastfeeding. It is 25 mcg (1,000 IU) for babies up to 6 months, 38 mcg (1,500 IU) from 7 to 12 months, 63 mcg (2,500 IU) at ages 1 to 3 and 75 mcg (3,000 IU) at ages 4 to 8. Signs of toxicity are unlikely below 250 mcg (10,000 IU) a day, but NIH notes that even intakes below the upper limit might cause harm over time.^1,9

The upper limit for magnesium from supplements and medicines is 350 mg a day for adults. It does not count magnesium in food and drinks.^2,10

The upper limit for adults is 40 mg of zinc a day from all sources: food, drinks, supplements and medicines, including during pregnancy and breastfeeding. It is 34 mg for teens aged 14 to 18 and lower for children. It is set to protect copper status and does not apply to people given zinc as medical treatment by a doctor.^3,11

The US upper limit for vitamin B6 is 100 mg a day for adults, counting food and supplements together. It is 80 mg for ages 14 to 18, 60 mg at 9 to 13, 40 mg at 4 to 8 and 30 mg at 1 to 3. In 2023 the European Food Safety Authority set a lower adult limit of 12 mg a day, including during pregnancy and breastfeeding. The US limit does not apply to people taking B6 for medical reasons under a doctor's care.^4,7,12

The upper limit for niacin from supplements and medicines is 35 mg a day for adults, including during pregnancy and breastfeeding. It is 30 mg for ages 14 to 18, 20 mg at 9 to 13, 15 mg at 4 to 8 and 10 mg at 1 to 3. It is set at the level linked to flushing, covers both nicotinic acid and nicotinamide, does not count niacin in food, and does not apply to people taking niacin under medical supervision.^5,13

No tolerable upper intake level is set for creatine. NIH reports few safety concerns at 20 g a day for up to 7 days followed by 3 to 5 g a day, and says use for several years appears safe in healthy adults. The ISSN reports no harm in studies using up to 30 g a day for up to 5 years.^6,8

The checker uses the US figure for vitamin B6. The lower European figure is in the entry above.⁷

Who should ask first

You take any medicine. Several of these nutrients interact with common medicines, so ask a pharmacist before combining.
You are pregnant, nursing or under 19. The limits for children and teens are lower, and the checker uses the adult figures.
You have kidney disease. Magnesium and creatine both need a check first.
You also take products that are not ours, such as a multivitamin or a B complex. Add their amounts to the checker's totals yourself.

Questions people ask

Does the checker count the vitamins in my food?

No. It adds up the labels of our products only. Some limits, such as vitamin D's 100 mcg, count food too, so your real total can be higher.¹

Why does it flag two creatine products when creatine has no upper limit?

No upper limit is set for creatine. The check is there to flag two creatine products taken on the same day, because a second full dose goes past the 3 to 5 g a day used in trials after a loading phase.^6,8

Can I trust a result with no notes?

A result with no notes only means that the totals from our products do not reach a limit the checker tracks. Food, other supplements and medicines are not counted.

What happens if I go over a limit?

It depends on the nutrient. High magnesium from supplements can cause diarrhea, nausea and abdominal cramping, zinc at 50 mg a day or more for weeks can block copper absorption, and too much vitamin D raises blood calcium.^1,2,3,9,11

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Sources

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