Supplements are a majority habit in this country. A 2021 data brief from the CDC’s National Center for Health Statistics, drawing on the 2017-2018 national health survey, put it at 57.6% of adults 20 and older in the previous 30 days. The over-60 figure is the one to sit with: 24.9% had four or more going at once.
Most of those bottles carry a Supplement Facts panel, and the panel looks like it’s telling you everything. Serving size, amounts, percentages, a tidy box of numbers.
Then you hit a line that reads something like “Focus Blend 1,500 mg,” with five ingredients listed underneath and no amounts next to any of them. That’s a proprietary blend. It’s completely legal. It also means you can’t tell how much of any one of those five ingredients you’re buying.
A 2019 analysis published in Nutrients examined the 100 top-selling pre-workout supplements and found an average of 18.4 ingredients per product, of which an average of 8.1 sat inside proprietary blends at undisclosed quantities. Across the whole sample, 44.3% of listed ingredients carried no individual amount.
This article covers how the panel is built, what it must show, and the places it’s allowed to stay quiet.
What the panel has to show
The Food and Drug Administration’s Dietary Supplement Labeling Guide sets the structure. The panel must carry the names and quantities of dietary ingredients, the serving size, and servings per container.
Serving size is defined in a way that catches people out. It’s the maximum amount the label recommends per eating occasion. Take the top of any range. A label reading “one to three tablets with breakfast” has set its serving at three. If the label recommends no particular amount, the serving is one unit: a tablet, a capsule, a packet, a teaspoonful.
That definition drives the arithmetic you do next. The amounts in the panel describe one serving, and a serving might be four capsules. Four capsules per serving turns a 120-count bottle into 30 servings.
Servings per container is required, but FDA allows it to be left off when it would simply restate the net quantity. A bottle of 100 tablets with a one-tablet serving doesn’t need a separate line saying 100 servings.
Certain nutrients have to be declared when they’re present in measurable amounts, including calories, total fat, saturated fat, cholesterol, sodium, total carbohydrate, dietary fiber, sugars, protein, vitamin A, vitamin C, calcium and iron. Other vitamins and minerals only have to appear if they were added for supplementation or if the label makes a claim about them.
Binders, excipients and fillers don’t belong in the panel at all. They go in the ingredient statement printed below it, which is a separate reading skill covered in this library’s article on ingredient lists.
Percent Daily Value, and the asterisk that means nothing is known
The %DV column is the part most readers trust, and it’s also the part that runs out.
FDA describes Daily Values as the recommended amounts of nutrients to consume, or not to exceed, each day. The percent Daily Value tells you how much of that reference amount one serving delivers. The calculation is the amount divided by the Daily Value, multiplied by 100, rounded to the nearest whole percent. When a declared amount works out to less than half a percent, the label shows “Less than 1%” instead of zero.
FDA’s general guideposts for reading those percentages are worth memorizing: 5% of a Daily Value or less per serving is a low amount, and 20% or more is a high amount.
This is the catch. Daily Values exist only for nutrients FDA has set them for. Most of the ingredients that sell supplements, meaning botanicals, amino acids, enzymes and specialty compounds, don’t have one. For those, 21 CFR 101.36 requires a symbol, usually an asterisk, pointing to a footnote that reads “Daily Value not established.”
Readers routinely misread that footnote as a warning or a quality flag. It’s neither. It means FDA hasn’t set a reference intake for that substance, usually because the evidence isn’t there to set one. The asterisk is a statement about the state of the science, not a judgment on the product.
The proprietary blend, and exactly what it withholds
This is the part worth memorizing.
When a manufacturer groups ingredients into a blend, FDA’s rules let the label call that group a Proprietary Blend, or give it a descriptive or fanciful name. The number printed on that line is, in the words of 21 CFR 101.36, “the total weight of all other dietary ingredients contained in the proprietary blend.”
Underneath the blend name, indented, the individual ingredients are listed in descending order of predominance by weight, each carrying the “Daily Value not established” symbol. No individual amounts appear anywhere.
One exception matters a lot. Ingredients that do have established Daily Values, meaning the familiar vitamins and minerals, have to be declared separately with their own weights. They can’t be folded into the blend. So a blend can conceal 400 milligrams of a botanical extract, but it can’t conceal the vitamin B6.
Now the arithmetic, using invented round numbers.
Say a label reads “Focus Blend 1,500 mg” with five ingredients listed beneath it in descending order. What do you know?
You know the five together weigh 1,500 milligrams. You know their rank order. And you know the first one is at least 300 milligrams, because if five things sum to 1,500 and the first is the largest, it can’t fall below the average.
That’s the whole list. The split could be 300 milligrams each, evenly. It could just as legally be 1,484 milligrams of the first ingredient and 4 milligrams each of the other four, which also sums to 1,500 and also sits in descending order.
Comparison across products breaks the same way. Suppose one product plainly declares 200 milligrams of an ingredient, and a competitor puts the same ingredient second in a 1,000-milligram blend of four. In that blend, the second ingredient can be at most 500 milligrams, because it can’t exceed the first and the two together can’t exceed the total. It can also be almost nothing, if the first ingredient accounts for 999 of the 1,000. Somewhere between a trace and 500 milligrams is a shrug, not a comparison.
Why blends exist, and why that isn’t automatically a scam
Fairness matters here, because the honest answer has two sides.
A formula is one of the few things a supplement company owns. Ratios are easy to copy once they’re printed. A blend keeps exact proportions out of a competitor’s hands and lets a manufacturer adjust them between production runs without reprinting labels. Contract manufacturers often build formulas for several brands at once, and the blend structure is how those proportions stay confidential. None of that is fraud, and plenty of companies with clean manufacturing records use blends.
The cost lands entirely on you. A blend removes your ability to do three things: compare dose across products, check whether an ingredient is present at an amount anyone has studied, and work out what you’re paying per milligram of the thing you came for.
The 2019 pre-workout analysis in Nutrients shows the scale of that. Across those 100 products, beta-alanine appeared in 87% of formulas at an average of 2.0 grams per serving, which the authors noted fell below the dose generally reported as effective. When an ingredient like that sits inside a blend, you can’t even run the check.
A companion 2022 analysis in Nutrients looked at 75 top-selling energy drinks and energy shots and found 15 of them carried proprietary blends with undisclosed ingredient amounts. Taurine turned up in roughly 37% of the products, and in those cases the amount wasn’t disclosed. In the same sample, among the two-thirds of products declaring vitamin B12, the average was more than 5,000% of the Daily Value. A very high percentage is not, by itself, a measure of value.
A reasonable position: a blend isn’t evidence of bad faith, but it’s a good reason to rank a product below a comparable one that discloses everything. You’re paying for a number you can’t see.
The elemental-weight rule changes every number you compare
This rule fixes a problem most readers don’t know exists.
21 CFR 101.36 requires that the quantity declared for a vitamin or mineral be the weight of the dietary ingredient itself, not the weight of the compound it came from. The regulation’s own example is calcium: the panel declares the weight of calcium, not the weight of calcium carbonate.
That distinction is large. Weigh out 1,000 milligrams of calcium carbonate and roughly 400 milligrams of it is calcium. Do the same with calcium citrate and you get about 210. The percentages behind that math, about 40% for carbonate and about 21% for citrate, come from the NIH Office of Dietary Supplements.
If labels declared compound weight instead, a carbonate product would look nearly twice as strong as a citrate product delivering the same calcium. Because the rule requires elemental weight, both panels report the same thing, and the comparison is real.
Where the source compound appears is optional. FDA allows a label to identify it in parentheses inside the panel, written as calcium followed by “as calcium carbonate.” If it isn’t shown there, it has to appear in the ingredient statement below the panel instead.
That parenthesis is worth hunting for even though the headline number is already corrected, because form affects more than weight. The Office of Dietary Supplements notes that calcium carbonate depends on stomach acid to dissolve and is better taken with a meal, while calcium citrate is less dependent on stomach acid and can be taken without food. It also reports that the share of calcium absorbed drops as the single dose rises: roughly 36% of a 300-milligram dose, compared with about 28% of a 1,000-milligram dose.
Two panels can both say 500 milligrams of calcium and still behave differently in a person. The number is comparable. The result isn’t.
Extracts, and the numbers that look bigger than they are
Botanical ingredients are where panel numbers get slippery, and the rules here are more specific than most readers realize.
Under 21 CFR 101.36, a liquid extract whose solvent hasn’t been removed is declared by the volume or weight of the total extract. A dried extract, where the solvent is gone, is declared by the weight of the dried extract. FDA’s labeling guide adds that liquid extracts should state the condition of the starting material, such as fresh, and may include concentration and solvent detail in a format pairing the total extract with the weight of starting material and the volume of solvent used.
Why this matters: 500 milligrams of a dried extract and 500 milligrams of powdered whole herb are not the same quantity of plant. An extract concentrates some constituents and leaves others behind, at a ratio that may or may not be printed. Two products can show identical milligram figures and deliver very different amounts of whatever you’re after.
FDA’s rules also permit specific constituents to be listed, indented under the ingredient, with their weights per serving. A label that does that is giving you more than it has to.
Evidence sits on top of all of this, not inside it. For most botanical ingredients, the human research is preliminary or insufficient rather than settled, and long traditional use is history rather than clinical evidence of effect. The panel can’t tell those apart, because it isn’t trying to.
What’s printed versus what’s in the capsule
The panel is a declaration. It isn’t a measurement of the bottle in your hand.
FDA’s labeling guide sets the compliance expectation plainly: an added dietary ingredient has to be present at 100% of the declared amount, apart from analytical variation, while a naturally occurring dietary ingredient has to be present at 80% of the declared value.
What manufacturers do is overshoot. A 2016 study in the American Journal of Clinical Nutrition, carried out by researchers at USDA and the NIH Office of Dietary Supplements, bought adult multivitamin and mineral products under a national sampling plan and chemically analyzed them. Measured content exceeded the labeled amount for every ingredient except thiamin. The predicted average excess ran from about 1.5% to 13% for a group including magnesium, niacin, potassium, folic acid, riboflavin, vitamin B-12, vitamin C and vitamin E, and reached roughly 25% for selenium and iodine.
Those overages exist for a practical reason. Nutrients degrade on the shelf, so manufacturers add extra to make sure the product still meets its label at the end of its shelf life. The researchers’ point was that intake estimates built from labels understate what people are really taking, and that most of those products already met Recommended Dietary Allowances before the extra was added.
None of this is visible on the panel. Whether the contents of your specific lot match the label is a testing question, and how products get tested is covered separately in this library.
Three questions to ask of any panel, and what it never tells you
Before you buy, run the panel through three questions.
1. What is one serving, and how many are in here? Find the serving size first, then divide the count by it. If a serving is three capsules and the bottle holds 90, you have 30 days, not 90. Multi-capsule servings are the most common reason a bottle empties faster than people expect.
2. Can I see an amount for the ingredient I came for? If the one ingredient that made you pick up the bottle sits inside a blend, you can’t know its dose. If a competing product discloses that amount, that’s a genuine difference between the two, and it cost the disclosing company something to be open about it.
3. How much of the formula is under the asterisk? Count the ingredients carrying “Daily Value not established.” That’s the portion of the product where no federal reference amount exists and, usually, where the evidence is thinnest.
Now the honest limits. A Supplement Facts panel reports identity and quantity. It doesn’t report bioavailability, meaning how much of a dose reaches your bloodstream. It doesn’t report quality, purity or the result of any test. It doesn’t report whether a dose matches the amount used in research, and it certainly doesn’t report whether that research found anything.
It also doesn’t report risk. The NIH Office of Dietary Supplements points out that supplements don’t need FDA approval before they’re sold, that a company only has to give FDA safety evidence in advance when a product contains a dietary ingredient that wasn’t on the US market before October 15, 1994, and that the agency mostly acts after a problem surfaces.
Some of those risks are specific, and the Office of Dietary Supplements names them. Warfarin loses some of its effect when vitamin K goes up. St. John’s wort pushes the body to clear many medicines faster. Some supplements raise bleeding risk or change how you respond to anesthesia, which is why a surgical team needs a complete list well ahead of a procedure rather than on the morning of.
So here’s the practical move. If you take a prescription medication, are pregnant, have surgery scheduled, or are one of the roughly one in four adults over 60 taking four or more products at once, bring the actual bottles to a pharmacist or your clinician and have them read the panels with you. Pharmacists do this routinely, at no charge, and they’re very good at it.
And the single most useful habit from all of this: when a panel hides an amount inside a blend, treat the missing number as information. A company that discloses its doses has handed you something to evaluate. A company that doesn’t has handed you a weight and a word.
Sources
- U.S. Food and Drug Administration. “Dietary Supplement Labeling Guide: Chapter IV, Nutrition Labeling.” fda.gov
- U.S. Food and Drug Administration. “Dietary Supplement Labeling Guide: Chapter V, Ingredient Labeling.” fda.gov
- U.S. Government Publishing Office / National Archives (eCFR). “21 CFR 101.36, Nutrition labeling of dietary supplements.” ecfr.gov
- U.S. Food and Drug Administration. “Daily Value on the Nutrition and Supplement Facts Labels.” fda.gov
- National Institutes of Health, Office of Dietary Supplements. “Dietary Supplements: What You Need to Know.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Calcium: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Dietary Supplement Fact Sheets.” ods.od.nih.gov
- Centers for Disease Control and Prevention, National Center for Health Statistics. “Data Brief No. 399: Dietary Supplement Use Among Adults, United States, 2017-2018.” cdc.gov
- PubMed. “Jagim AR, Harty PS, Camic CL. "Common Ingredient Profiles of Multi-Ingredient Pre-Workout Supplements." Nutrients, 2019. PubMed. DOI: 10.3390/nu11020254.” doi.org
- PubMed. “Jagim AR, Harty PS, Barakat AR, et al. "Prevalence and Amounts of Common Ingredients Found in Energy Drinks and Shots." Nutrients, 2022. PubMed. DOI: 10.3390/nu14020314.” doi.org
- PubMed. “Andrews KW, Roseland JM, Gusev PA, et al. "Analytical ingredient content and variability of adult multivitamin/mineral products: national estimates for the Dietary Supplement Ingredient Database." American Journal of Clinical Nutrition, 2017. PubMed. DOI: 10.3945/ajcn.116.134544.” doi.org