At a glance
| Where | Pros | Cons | Best for |
|---|---|---|---|
| Costco (Kirkland) | Big bottles, usually low cost per serving, many products carry the USP Verified mark | Membership required, fewer choices, very large bottles | People taking basics like a multivitamin, vitamin D or fish oil long term |
| Amazon | The biggest selection, plus Subscribe & Save discounts | Third-party sellers mixed in, with a risk of fakes or old stock | Shoppers who know how to check the seller |
| iHerb | Wide range, including international and small brands, frequent sales, ships overseas | You have to follow customs rules | People who can't find a brand in stores, or who ship to family abroad |
| Walmart, Target, CVS, Walgreens | Buy it today, store brands are usually cheaper | Selection varies by store | When you need it now or want to see the bottle in person |
| Brand's own website | Least worry about fakes | Often close to full price | People who stick with one brand |
Costco: cheap basics, but you need a membership
Costco's own brand, Kirkland Signature, comes in big bottles and is usually cheap per serving. Many product pages show the USP Verified mark. According to Costco, the mark means the product:
- Contains the ingredients listed on the label in the stated amounts
- Does not contain harmful levels of certain contaminants, such as heavy metals and pesticides
- Breaks down and dissolves within a set time
- Is made following FDA Good Manufacturing Practices (GMP)
| What to check | Details |
|---|---|
| Membership fee (Costco website, October 2026) | Gold Star $65/year · Executive $130/year, plus tax (may change) |
| Selection | Smaller than a drugstore. Mostly basic supplements |
| Bottle size | Often 300–500 tablets. Make sure you can finish it before it expires |
Amazon: the most choice, but check the seller
Amazon carries almost every brand, but products sold by Amazon and by third-party sellers show up side by side. Look at the small print under the cart button.
| What it says | What it means | Our take |
|---|---|---|
| Ships from Amazon · Sold by Amazon | Sold and shipped by Amazon itself | Safest choice |
| Sold by the brand name (official store) | Sold by the brand or its official seller | Fine |
| Sold by a seller you don't recognize | Third-party seller | Check if they're on the brand's "Where to Buy" list |
With Subscribe & Save, Amazon's help page says any discount shows on the product page, and you unlock extra savings when five subscriptions arrive together at one address. But it also says discounts and prices can change at any time. Check the price in the reminder email before each delivery, and skip or cancel if you don't need it.
iHerb: wide brand range, good for shipping abroad
iHerb sells a wide range of brands, including international and small brands that are hard to find in US stores. It runs frequent sales and promo codes, so buying during a sale can help.
iHerb also ships to many countries, so you can send supplements straight to family overseas. For example, iHerb's South Korea shipping page (October 2026) says:
- The recipient needs a Personal Customs Clearance Code (PCCC), and the registered name, phone number and address must match the order
- If orders from the same overseas seller on the same day total more than $150, import duties may apply (orders close to the limit may also be taxed because of exchange rates)
- Import rules, such as quantity limits on supplements, are set by the destination country's customs and food safety agencies. Check them before you ship
Walmart, Target, CVS, Walgreens: when you need it today
The biggest perk of a local store is that you can buy it today. Each chain has its own store brand, which is usually cheaper.
| Store | Store brand |
|---|---|
| Walmart | Equate |
| Target | up&up |
| CVS | CVS Health |
| Walgreens | Walgreens |
- Store brands are not all the same quality. Check the label for a third-party seal like USP Verified or NSF yourself
- Drugstore chains often run deals like "buy one, get one free" and rewards programs
- Walmart and Target websites also include third-party sellers. Look for wording like "Sold and shipped by Walmart"
Brand websites: the surest way to get the real thing
If you stick with one brand, buying from its official website is the least worry when it comes to fakes.
- Prices are often close to full price, but some brands offer first-order or subscription discounts
- The brand's "Where to Buy" list tells you which Amazon sellers and stores are authorized
- Some brands don't sell online at all. If you see one of those online, someone is reselling it
Checklist to avoid fake or tainted supplements
The FDA does not approve supplements for safety or effectiveness before they're sold. The FDA has found more than 1,000 products sold as "supplements" with hidden drug ingredients that can harm you, and it warns these are sold online, in stores and at gas stations. The most common types are:
- Sexual enhancement · weight loss · bodybuilding · joint pain · blood sugar · sleep products
Check before you buy and after it arrives.
- Is the seller Amazon, the brand, or an official seller the brand lists?
- Is the price far lower than everywhere else?
- Does it make claims like "works in 30 minutes" or "replaces your prescription"?
- Is the label in a foreign language but says "Made in USA," or does it use the FDA logo?
- Does the label list the company name, address and contact information?
- Does it carry a third-party seal like USP Verified or NSF?
- After it arrives, is there a lot number and expiration date, with plenty of time left?
- Do the packaging, seal and pill color and shape look normal? Any typos on the label?
Compare cost per serving, not bottle price
A bottle can look cheap, but if a serving is 2 or 3 pills, it may cost more in the end. The math is simple.
Cost per serving = bottle price ÷ (total pills ÷ pills per serving)
| Product A | Product B | |
|---|---|---|
| Pills per bottle | 120 | 90 |
| Serving (Serving Size on the label) | 2 capsules | 1 capsule |
| Days it actually lasts | 60 days | 90 days |
Product A has more pills, but Product B lasts 30 days longer.
- If the amount per serving differs, compare the dose too. For example, magnesium should be compared by elemental amount → elemental magnesium chart
- A big bottle is only a deal if you can finish it before it expires. For probiotics and fish oil, check storage instructions too
Where can you use an HSA or FSA card?
What matters first is whether the product counts as a medical expense, not the store. Most supplements taken for general health don't qualify for an HSA or FSA.
| Situation | Payment |
|---|---|
| The product is marked "FSA or HSA eligible" | Stores and websites that use that label often let you pay with the card directly |
| A doctor recommends it to treat a diagnosed condition + Letter of Medical Necessity (LMN) | Paying with a regular card and getting reimbursed with your receipt and LMN is the surest way |
| Just for general health | Doesn't qualify |
We cover the full rules in Can you use HSA or FSA for supplements?.
Bottom line
- Taking basics for a long time → Costco Kirkland (see our comparison)
- Need a wide selection → Amazon, but make sure the seller is Amazon or the brand
- International brands or shipping to family abroad → iHerb, and check customs rules
- Need it today → Walmart, Target, CVS, Walgreens, and check the label for a seal
- Wherever you buy → look at three things: cost per serving · expiration date · third-party seal
- Not sure what to take yet → Check what your body needs
If you take medications, talk to your doctor or pharmacist before starting a new supplement.
Related supplements
Frequently asked questions
Can I buy Kirkland supplements without a Costco membership?
You may see Kirkland products on sites like Amazon, but they're often resold by other sellers, not sold by Costco. They may cost more, and it can be hard to know how they were stored or when they expire, so always check the seller and the expiration date.
How can I tell if a supplement from Amazon is fake?
First, check your order to see if the seller ("Sold by") was Amazon or the brand's official store. When it arrives, check the lot number, expiration date, safety seal, the pills' color, size and shape, and any typos on the label. If something looks different, don't take it. Return it and report it to Amazon. You can also contact the brand's customer service with the lot number and ask.
Can I ship supplements to family overseas through iHerb?
Yes, iHerb ships to many countries. For South Korea, for example, the recipient needs a Personal Customs Clearance Code, and duties may apply if same-day orders from the same seller total more than $150 (per iHerb's page, October 2026). Import rules like quantity limits or banned ingredients can change, so check the destination country's customs and food safety agencies.
Are store brands like Equate and up&up trustworthy?
Judge by the product label, not the brand name. A third-party seal like USP Verified or NSF means an outside group checked that the listed ingredients are in the bottle in the listed amounts. Even within one store brand, some products have a seal and some don't.
Is Amazon Subscribe & Save always a better deal?
No. Amazon's own help page says discounts and prices can change at any time. Check the price in the reminder email before each delivery and compare the cost per serving with other stores. You can skip or cancel anytime.
Sources
- Costco — Join Costco (membership types and annual fees)
- Costco — Kirkland Signature Daily Multi (USP Verified explanation)
- Amazon Customer Service — Subscribe & Save
- iHerb — Shipping to Korea (shipping and customs)
- FDA — Medication Health Fraud
- FDA — Tainted Products Marketed as Dietary Supplements and Foods (2025)
- FDA — Information for Consumers on Using Dietary Supplements
- ConsumerLab — How to avoid counterfeit supplements
Last updated 2026-10-20