Supplement Basics

What dietary supplements can do, how to read the label, and what to check before adding one to your routine.

You go to the store for vitamin D and find three strengths, two forms, and a multivitamin that already contains it. At home, you remember that your calcium tablets contain vitamin D, too. Now the question is less about which bottle looks best and more about how much you’re already getting, why you want more, and whether you need another product at all.

That’s a useful way to approach any supplement. Start with the reason you’re taking it. Then check the ingredient, the amount you’ll actually take, and how it fits with everything else you use. A supplement can help cover a dietary gap or address a specific medical need. Its value depends on the ingredient, the dose, and the person taking it. Consumer

What is a dietary supplement?

Dietary supplements are products intended to add something to your diet. They include vitamins and minerals, such as vitamin B12 and iron, as well as herbs, amino acids, probiotics, fish oils, and other ingredients. They come as capsules, tablets, gummies, powders, and liquids. In the United States, products sold as dietary supplements generally carry a Supplement Facts panel. Consumer

The form can make a difference in how easy a product is to use. You might prefer a liquid if you have trouble swallowing tablets or a powder if you already make a morning smoothie. Check the label before assuming two forms deliver the same amount. A gummy and a capsule sold under similar names can have different formulas, serving sizes, and directions. Consumer

Some supplements are single-ingredient products. Others combine several ingredients, as multivitamins and many sleep or fitness formulas do. If your goal is to add one nutrient, a single-ingredient product can make it easier to see what you’re getting. If you’re considering a blend, look at whether each ingredient serves a purpose for you and whether any duplicate something you already take. Consumer

When might a supplement be useful?

When your diet leaves a specific gap

If you eat a vegan diet, for example, it’s worth checking where you get vitamin B12. It occurs naturally in animal foods and is added to some plant milks, cereals, and other fortified products. Look at what you eat consistently. A fortified food you have most days may contribute more than a product you buy occasionally. If you’re unsure whether you get enough, ask a clinician or registered dietitian how fortified foods or a supplement could fit your routine. ods.od.nih.gov

When a clinician identifies a deficiency

A confirmed deficiency may need a different dose or form from what you’d find in a routine multivitamin. The cause matters, too. Low B12 because you eat few foods that contain it is a different situation from low B12 because you have difficulty absorbing it. If a test shows a deficiency, ask what could be contributing, how long you’ll need treatment, and when to follow up. ods.od.nih.gov

When there’s a recommendation for your stage of life

Folic acid is one example. The CDC recommends 400 micrograms of folic acid daily for people who can become pregnant to help prevent neural tube defects. Getting enough before pregnancy matters because the neural tube develops early. If you’re choosing a prenatal vitamin, check the label for the folic acid amount and ask your clinician what fits your medical history. CDC

When you have a specific goal and relevant evidence

A product may be marketed for sleep, exercise, digestion, or focus. Turn the claim into a question you can answer. “Supports performance” is broad. “Does this ingredient help people doing the type of training I do?” gives you a way to judge the research. Check whether the studies used the same ingredient form, a comparable dose, and an outcome you care about. If the product combines several ingredients, a study on one ingredient tells you only part of the story. Consumer

How to read the Supplement Facts panel

Start with the serving size and directions

The serving size may be one tablet, two gummies, or a scoop of powder. The amounts in the panel generally refer to that serving. The directions tell you how often the manufacturer suggests taking it. Read both before comparing products or adding up your daily intake. Consumer

For example, imagine two bottles that each contain 60 capsules:

Product A provides more of the ingredient per labeled serving. Product B provides more per capsule and has twice as many servings in the bottle. If you’re comparing price, check the cost per serving. If a clinician has given you a target amount, check which product matches it and confirm how to take it. The numbers above are illustrative, not a dose recommendation.

Check the ingredient name, form, and units

Compare the full ingredient name. An herbal label might list a plant powder or a concentrated extract. A fish oil label may state the total weight of the oil and separately show EPA and DHA, the omega-3 fatty acids you may be looking for. If you’re buying the product for its EPA and DHA, those individual amounts tell you more than the total oil weight. Consumer

Read the units carefully. One milligram (mg) equals 1,000 micrograms (mcg). Some nutrients, including vitamin D, may also be expressed in international units (IU). The conversion from IU depends on the nutrient. If your clinician recommended an amount in one unit and the bottle uses another, ask a pharmacist to confirm the match. Consumer

Know what Percent Daily Value tells you

The Percent Daily Value (%DV) shows how much one serving provides relative to a daily labeling reference. If a product lists 100% DV for a nutrient, one serving supplies the full reference amount. Your individual needs and the amount you already get from food can differ. A higher percentage doesn’t establish that the product is more useful for you. Some ingredients don’t have an established Daily Value, so their labels may list an amount without a percentage. www.fda.gov

Some nutrients also have a Tolerable Upper Intake Level, which is a separate reference used to assess the risk of getting too much. Depending on the nutrient, the limit may apply to all sources or to specific sources such as supplements and fortified foods. This is one reason to check totals before combining a multivitamin with high-dose single nutrients. If a clinician prescribed a higher dose for a specific reason, ask how long you should take it and what follow-up you’ll need. Consumer

Look for individual amounts in blends

A label that lists a 600 mg proprietary blend may give the total weight and the names of the ingredients without stating how much of each is present. If you want to compare one ingredient with a published study or check how much you’re getting across products, the blend total won’t give you enough information. A label that lists the individual amounts makes that comparison easier. www.fda.gov

Also read the Other Ingredients list. It can tell you about capsule materials, sweeteners, flavorings, and other ingredients that may matter if you have an allergy or dietary restriction. If you can’t determine whether a product is suitable from the label, ask the manufacturer or a pharmacist before using it. Consumer

How to judge supplement quality and marketing claims

In the United States, the FDA generally does not approve dietary supplements for safety and effectiveness before they are sold. Manufacturers are responsible for meeting applicable safety and labeling requirements, and the FDA can take action when a product is adulterated or misbranded. A bottle’s presence on a shelf or a major marketplace doesn’t tell you how strong the evidence is for its claims. www.fda.gov

Independent quality programs, such as USP and NSF, can give you more information about a product. Depending on the program, verification may cover whether the contents match the label or whether the product meets limits for certain contaminants. Check the exact product in the certifier’s directory and see what the certification covers. Quality testing can tell you something about what’s in the bottle. Evidence of a health benefit comes from studies that measure that benefit. Consumer

When you see a claim, look for the information that would let you evaluate it:

Suppose a review says a supplement helped someone sleep better in three days. That’s a report of one person’s experience. To judge what you might expect, look for a study with a comparison group, clear dosing, and a measure that matters to you, such as how long it takes to fall asleep or how often you wake. Then see whether the product you’re considering matches what was tested. Consumer

Check for overlap and interactions

Put everything you take on the same list, including multivitamins, single nutrients, herbal products, fortified powders, and supplements you use only occasionally. Write down the amount per serving and how many servings you take. A nutrient that looks modest on one label can add up when it’s in three products. If you’re reviewing the list with a pharmacist, photos of the labels are more useful than product names alone. Consumer

Some interactions are easy to miss. Vitamin K can affect warfarin treatment, so talk with your care team before making a substantial change to your intake from food or supplements. Ginkgo may increase bleeding risk in people who take anticoagulants. Also tell your healthcare team if you take biotin, which is often included in hair and nail products. Biotin can interfere with certain lab tests, including some tests used to help diagnose a heart attack. Ask the clinician or lab what to do before a scheduled test. Consumer

A review is especially helpful if you take prescription medication, have surgery coming up, are pregnant or breastfeeding, or are choosing a supplement for a child. Ask a pharmacist or clinician about the exact product, the amount you plan to take, and whether you need to separate it from other medicines. If you’ve already been given a supplement as part of your care plan, check before changing it. Consumer

What to do after you start a supplement

Know what you’ll use to judge whether it’s helping. If you’re treating a deficiency, your clinician may recommend a repeat test or ask you to watch for specific changes. If you’re trying a supplement for a less concrete goal, agree on what a meaningful improvement would look like and when you’ll reassess. “I want to feel better” is hard to evaluate. “I want to see whether this helps with the symptom we discussed over the next month” gives you something to revisit. ods.od.nih.gov

If you add several products at once, it can be difficult to tell which one helped or caused a side effect. When your care plan allows, introduce one change at a time and note the product, amount, and start date. Keep the packaging if you develop a reaction, since the ingredient list and lot number may help identify what you took. Consumer

If you suspect a supplement caused a serious reaction, stop taking it and seek medical care. Trouble breathing or swelling of the lips, tongue, or throat calls for emergency help. In the U.S., you can also report a suspected reaction to the FDA after getting the care you need. www.fda.gov

Common questions about dietary supplements

Do I need a multivitamin every day?

It depends on what you regularly eat and whether you have specific nutrient needs. A multivitamin may help cover some gaps, but formulas vary. Check what’s included, how much you get per serving, and whether the product overlaps with anything you already take. If you’re trying to address one particular nutrient, ask whether a targeted approach makes sense. Consumer

Are gummies as good as tablets?

The answer depends on the formula and the dose. Compare the active ingredients and amounts per serving, then see how many gummies or tablets you’d need. Look at other ingredients if added sugar, sweeteners, or gelatin matter to you. Store gummies and other supplements out of children’s reach, especially if they look or taste like candy. Consumer

Should I take supplements with food?

It depends on the ingredient and what else you take. Food can affect absorption or how well you tolerate certain products. If you take several medicines or supplements in the morning, ask your pharmacist to help you work out the timing. Bring the labels so they can check the actual ingredients and directions. Consumer

Is the more expensive product better?

Compare the ingredient, form, dose, number of servings, and any quality verification you can check. A higher price may reflect a different formulation or more servings, but you won’t know by comparing the front labels alone. For example, a $24 bottle with 30 servings costs $0.80 per serving, while a $30 bottle with 60 servings costs $0.50 per serving. Compare prices after you’ve found products that fit your needs.

A quick checklist before you buy

1. Name the reason. What gap, medical need, or specific goal are you trying to address?
2. Check the amount. How much of the ingredient is in each serving, and how many servings would you take?
3. Compare the evidence with the label. Does the research use the same form and a comparable dose?
4. Review what you already take. Check for overlap, interactions, and any upcoming tests or procedures.
5. Decide how you’ll follow up. Know when you’ll reassess and who to ask if you notice a side effect.

Try the checklist with a supplement you already own. Turn it over, find the serving size, and compare it with the amount you actually take. Then set it beside your other products and look for repeated ingredients. You may find you already have what you need, or you may find one specific question to take to your pharmacist before your next purchase.