How to Read a Supplement Label (and Spot Red Flags)

In the US, dietary supplements don’t need FDA approval before they’re sold. The manufacturer is responsible for making sure a product is safe and its label is truthful, and the FDA usually steps in only after problems appear. That makes the label your main tool for judging what you’re buying.

This guide walks through a Supplement Facts label section by section, explains the units and terms that trip people up, shows how to spot a proprietary blend, and lists the red flags that should make you put a bottle back on the shelf. For more buying guides, see our supplement guides.

Who checks supplement labels?

Under US law, supplements are regulated more like foods than medicines. A company doesn’t have to prove to the FDA that a supplement works before selling it, and for most ingredients it doesn’t have to show the FDA safety data first either. The main exception is a “new dietary ingredient” that wasn’t sold before October 1994, which needs a safety notification.

Manufacturers must follow good manufacturing practices meant to ensure each product’s identity, purity, strength and composition. The FDA inspects facilities, monitors reports of harm and can force recalls, while the Federal Trade Commission polices advertising. In practice, though, the system relies heavily on companies following the rules, and the FDA regularly finds products with ingredients that aren’t on the label.

The label rules themselves are strict. Every supplement must have a “Supplement Facts” panel in a set format, and ingredients that are added must be present at 100% of the declared amount. That makes the panel the most dependable part of the package.

Reading the Supplement Facts panel

Work through the panel from top to bottom.

1. Serving size and servings per container

The serving size is the amount the manufacturer recommends per dose, and every number below it is per serving. This is the most commonly missed detail: a “1,000 mg” product may need two or three capsules to reach that amount. Divide the servings per container into the price to see the real cost per day.

2. Amount per serving

Each dietary ingredient is listed with its weight per serving, usually in milligrams (mg) or micrograms (mcg). For vitamins and minerals, this is the amount of the nutrient itself, not the compound it’s attached to. For example, “Calcium (as calcium carbonate) 500 mg” means 500 mg of calcium, not 500 mg of calcium carbonate.

3. % Daily Value

The % Daily Value (% DV) shows how much of the FDA’s reference amount for a nutrient one serving provides. Daily Values are set to cover most adults and children over 4. A product with 100% DV of vitamin C gives the full daily amount in one serving.

More than 100% isn’t necessarily a problem, as long as your total from food and supplements stays under the tolerable upper intake level (UL), the highest daily intake unlikely to cause harm. Some products contain several times the DV for nutrients like vitamin B12, which have no known upper limit, but much less margin exists for vitamin A, iron, zinc and vitamin B6.

Ingredients such as herbs, fish oil fatty acids, probiotics and creatine have no Daily Value. They’re marked with a symbol, usually an asterisk, that points to the footnote “Daily Value not established”.

4. The ingredient form

Look at the words in brackets after each nutrient, such as “as magnesium glycinate” or “as cholecalciferol”. The form affects how well a nutrient is absorbed, how likely it is to upset your stomach, and sometimes how much of the label amount you actually get. Our guide to types of magnesium shows how much this matters for one mineral.

5. Herbs and extracts

For herbal products, the panel should name the plant part used, such as root, leaf or seed. Extracts may also show a ratio (such as 10:1, meaning 10 g of herb made 1 g of extract) or a standardization, such as “standardized to 95% curcuminoids”. Standardization tells you the amount of a marker compound, which makes it easier to compare a product with the doses used in studies.

An example label, explained

Here’s how a typical vitamin D and magnesium label might read, with notes on what each line tells you.

Example for illustration only. % DV uses current FDA Daily Values: vitamin D 20 mcg, magnesium 420 mg, zinc 11 mg.

Note that the 250 mg of magnesium is already within the 350 mg upper limit for magnesium from supplements, but if you also take a separate magnesium product, you could go over it.

Units and forms that confuse people

US supplement labels switched to newer units after the FDA updated its labeling rules in 2016. Older bottles and some imported products still use the old ones.

• Vitamin D in mcg and IU: 1 mcg equals 40 IU. So 25 mcg is 1,000 IU, and 100 mcg is 4,000 IU, the adult upper limit.
• Vitamin A as mcg RAE: retinol activity equivalents account for the fact that beta-carotene converts to vitamin A less efficiently than retinol. The upper limit of 3,000 mcg applies to preformed vitamin A (retinol and retinyl esters), not beta-carotene.
• Vitamin E in mg: labels now show mg of alpha-tocopherol rather than IU.
• Folate as mcg DFE: dietary folate equivalents account for folic acid being better absorbed than natural folate. 400 mcg of folic acid is listed as 680 mcg DFE. The 1,000 mcg upper limit applies to folic acid itself.
• Elemental minerals: the panel lists the mineral itself, but front-of-pack marketing sometimes shows the weight of the whole compound, such as “500 mg magnesium citrate”, which contains far less actual magnesium.
• Probiotics in CFU: colony-forming units estimate the number of live microbes. Look for the count “at expiration” rather than “at manufacture”, since numbers fall over time.

Proprietary blends

A proprietary blend, sometimes called a “complex”, “matrix” or “formula”, is a mix of ingredients listed under one name with a single total weight. The ingredients must be listed in order from most to least by weight, but the label doesn’t have to say how much of each one is in the blend.

Companies say blends protect their recipes. The problem for you is that a “1,500 mg energy blend” might contain 1,400 mg of a cheap ingredient and a few milligrams of the ingredients that are actually backed by research. You can’t compare the doses with those used in studies, and you can’t tell if a stimulant like caffeine is present at a high dose.

Blends are common in pre-workouts, weight-loss products, “greens” powders and herbal formulas. If a product’s main selling point is an ingredient hidden inside a blend, look for a brand that discloses every dose.

Other ingredients and allergens

Below the panel, the “Other ingredients” list shows fillers, binders, capsule materials, flavors, colors and sweeteners. It’s worth a quick look:

• Capsule type: gelatin comes from animals; vegetarian capsules are usually made from cellulose (hypromellose).
• Sweeteners and sugar alcohols: gummies often contain several grams of sugar per serving, and sugar alcohols can cause bloating.
• Common fillers: ingredients such as microcrystalline cellulose, rice flour, silicon dioxide and magnesium stearate are used in small amounts and are generally considered safe.
• Allergens: US labels must declare the major food allergens, including milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, soy and sesame. Fish oil, glucosamine (often from shellfish) and whey protein are common sources.

Health claims: what labels can and can’t say

By law, a supplement label can’t claim to diagnose, treat, cure or prevent a disease. It can make “structure/function” claims about how a nutrient or ingredient affects the body, such as “supports healthy bones” or “helps maintain normal sleep”. Any such claim must carry this disclaimer:

“This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.”

That sentence means the FDA hasn’t checked whether the claim is true. “Supports immune health” might be backed by good research, or by none at all. A few FDA-authorized health claims exist, such as calcium and vitamin D for osteoporosis risk, but they’re less common.

Labels that suggest a product will cure arthritis, reverse diabetes, kill cancer cells or replace medicine are breaking the rules, and that alone is a reason to avoid the brand.

Third-party seals

Because the FDA doesn’t test products before they’re sold, independent testing programs are the best way to check quality. The main ones are:

Check a product’s listing on the certifier’s own website, since seals are sometimes used without permission.

A seal tells you the bottle contains what the label says and nothing harmful. It doesn’t mean the product works, that the dose is right for you, or that it’s safe with your medicines.

Be skeptical of phrases like “made in an FDA-approved facility”. The FDA doesn’t approve facilities. “Made in a GMP-certified facility” is better, though GMP compliance is required by law anyway.

Red flags

The FDA keeps a database of tainted products found to contain undeclared drugs, such as sibutramine in “natural” weight-loss pills. A product not appearing on the list doesn’t mean it’s safe. If you have a bad reaction, stop the product, see your doctor, and report it to the FDA’s MedWatch program.

Before taking a new supplement, show the label to your doctor or pharmacist, especially if you take medicines, are pregnant or breastfeeding, or have surgery coming up. Some interactions are serious: vitamin K can weaken the effect of warfarin, and St. John’s wort speeds the breakdown of many drugs, including birth control pills. Herbal weight-loss products can also carry real risks; our guides to goraka (garcinia) and hercampuri show why. See also our medical disclaimer.

Supplement label FAQ