In the US, supplements do not need FDA approval before they go on sale, and the label is largely the manufacturer's word. That puts the work of judging quality on you. This guide gives you eight practical checks, using real labels from the ten supplement stores we reviewed as examples. It is general buying guidance, not medical advice: talk to your doctor or pharmacist before starting anything, especially if you take medication, are pregnant, or have a health condition. ## 1. Start with a reason, ideally a test
The best supplement is one that fills a gap you actually have. Vitamin D, iron, and B12 levels can be measured with a blood test. Buying a high-dose product "just in case" is how people overshoot. Example: Celarity's D3 K2 10,000, sold through NuVision Health Center, provides 10,000 IU of vitamin D3, well above typical daily guidance. Our product note recommends it only for people whose doctor has checked their levels. ## 2. Read the Supplement Facts panel, not the front label
Look for three numbers: the amount of each active per serving, the number of units per serving, and the servings per container. - Serving size changes the math. Nature's Fusions Nutri Magnesium Glycinate delivers 480 mg of elemental magnesium, but that takes four capsules. You can take fewer for a lower dose. - Elemental versus compound weight. That same 480 mg comes from 3,600 mg of magnesium glycinate. Always compare elemental amounts. - Watch upper limits. 480 mg of supplemental magnesium is above the commonly cited upper limit for supplemental magnesium in adults (350 mg), which can cause digestive upset. Our product note flags this. ## 3. Prefer disclosed doses over proprietary blends
A "proprietary blend" lists ingredients but not how much of each. You cannot tell whether a dose is meaningful. Brands that publish exact amounts make comparison possible. Green Regimen ThermoLean, for example, lists 200 mg caffeine anhydrous and 200 mg of a ginger extract blend per capsule. Even there, the individual ginger extract amounts inside the branded blend are not broken out. ## 4. Look for third-party testing
Independent certification checks that a product contains what the label says and is not contaminated. Common marks include USP Verified and NSF Certified, and NSF Certified for Sport or Informed Sport for athletes who face drug testing. Two examples from our reviews:
- Celarity Creatine+ ($36.97, via NuVision) carries NSF Certified for Sport status. - Xymogen Omega MonoPure 900 EC ($59.99, via NuVision) is listed as IFOS five-star certified, a fish-oil-specific purity program. Compare that to Nature's Fusions Nutri Creatine: 100 servings of plain micronized creatine for $29.99, about 30 cents a serving, made and tested in the brand's own US facility but not sport-certified. If you are not drug-tested, plain creatine monohydrate is one of the most studied supplements and does not need a premium label. If you are tested, pay for the certification. ## 5. Check interactions and who should avoid it
Many supplements interact with medications. Examples straight from listings we reviewed:
- Vitamin K2 can interact with blood thinners such as warfarin. - Fish oil labels advise talking to a doctor if you take blood thinners. - Ashwagandha is not advised during pregnancy and can interact with thyroid, sedative, and immune medications. - High folate can mask a B12 deficiency. - Caffeine at 200 mg per capsule, as in ThermoLean, is about two cups of coffee, so do not stack it with other stimulants. High-dose biotin, such as the 10,000 mcg in a Mars By GHC hair chew, is also known to interfere with some lab tests, so tell your doctor before bloodwork. ## 6. Treat disease claims as a red flag
Supplements may make structure and function claims ("supports immune health") but not claims to treat or cure diseases. Product names that promise to fix a medical condition, or copy built around health trends, are a reason for more scrutiny. Nature's Fusions stands out for the opposite reason: its story page states plainly that essential oils do not cure diseases. When a listing cites a study, check whether it tested the finished product or just one ingredient. Green Regimen's SheVolve page notes its cited study tested the SheVari4 ingredient, not the product itself. ## 7. Compare price per serving, and ignore compare-at prices
Several stores we reviewed show compare-at prices far above the selling price, including Mars By GHC (three to four times higher on nearly every item) and Natural Cure Labs. Work out cost per serving instead. A few from our notes:
| Product | Price | Servings | Cost per serving |
|---|---|---|---|
| Nature's Fusions Nutri Creatine | $29.99 | 100 | About $0.30 |
| Nature's Fusions Nutri Methylfolate 1 mg | $14.99 | 120 | About $0.12 |
| Natural Cure Labs KSM-66 Ashwagandha with Magnesium | $17.95 | 30 | About $0.60 |
| Green Regimen ThermoLean | $19.99 | 30 | About $0.67 |
Natural Cure Labs also sells some formulas under a second label, Palmara Health, at a lower price; one listing says the Palmara version is the same product as the NCL version. Check both before buying. ## 8. Read the return policy before you open the bottle
Opened supplements are rarely returnable anywhere. Some stores go further: NuVision Health Center and Z-Stack Canada say all sales are final except damaged or wrong items, and Mars By GHC does not refund delivered products in good condition. Natural Cure Labs offers 60 days on unopened domestic orders. The Feed usually gives store credit or a replacement rather than cash, and opened specialty supplements over $40 are final sale. ## Where the stores we reviewed land
Most useful: The Feed (7.6) is a multi-brand retailer for endurance athletes where single servings from about $2 let you test gels, chews, and electrolytes before buying a box. Natural Cure Labs (7.0) has short ingredient lists, published US manufacturing, and free shipping over $30. Nature's Fusions (6.7) prices mainstream basics fairly and lists doses clearly, though we could not find its shipping or return policy. Fine with caveats: NuVision Health Center (6.0) for practitioner brands, if you accept final sale. Green Regimen (6.0) for its disclosed-dose capsules, though it publishes no shipping policy. Mars By GHC (5.9) for men's formulas, but read labels carefully and expect no returns. Caution: we do not recommend ordering from Sunleafy (5.2), Viva Nutra (5.3), or Z-Stack Canada (5.3) without first confirming terms by email; the first two have conflicting return terms, and Z-Stack Canada sells one product with final-sale terms. Obvi Canada (4.3) showed only a Coming Soon page when we checked. ## The short version
Know why you are taking it, read the facts panel, prefer disclosed doses and third-party testing, check interactions with your doctor, ignore inflated discounts, and price per serving. Buy one bottle before a bundle, because opened supplements almost never come back.