Finding the best supplement should be more than just a guessing game.

Supplement addicts, listen up! ConsumerLab.com, a third-party service that tests vitamins and supplements to see if they're delivering doses and nutrients as advertised, has just published its annual list of the most popular vitamin, mineral, and supplement brands.

Almost 11,000 people responded to this most recent ConsumerLab survey, and their picks for best supplements, based on overall customer satisfaction, include Life Extension, USANA, Costco's Kirkland brand, Nature Made, Trader Joe's Darwin brand, and CVS's store brand.

Voters also picked Barlean's as one of the best brands. Sold mostly at health food stores, Barlean's is one of only a few brands certified as GMO-free under the Non-GMO Project, and its omega-3 krill oils are sourced from fisheries certified as well managed.

If you're a supplements user, quality is important, no matter which vitamins you need. Tod Cooperman, MD, president of ConsumerLab, says they use these results to determine which brands and products to test later on in the year—which is important because supplements are largely unregulated. As a result, the Food and Drug Administration (FDA) has found everything from lead to cancer-causing preservatives in cheap supplements, and fish oil pills have been found to be contaminated with mercury, polychlorinated biphenyls (PCBs), and other industrial contaminants, just as fish are.

No matter which brand you prefer, here are a few things to keep in mind when shopping:

• Know your dosage. Anything—even water—can be hazardous in huge quantities, and many supplements contain megadoses of vitamins and minerals that you'd never find in food. Know the effective dosage for a particular vitamin or mineral before buying the supplement that delivers the highest level available, and then find out if you're deficient. After a study came out in the Archives of Internal Medicine finding that some supplements and multivitamins could lead to an early death, physicians warned that taking unnecessary supplements could do more harm than good.

• Eat food, not supplements. They're called "supplements" for a reason. Whole foods are packed with more than enough vitamins and minerals (in addition to other important components, like fiber) in forms and combinations that appear to be far more beneficial than those in vitamin pills. Eating lots of different foods means you get the whole complement of nutrients without ever setting foot in a supplement store.

• Talk to your pharmacist. Some dietary and herbal supplements can interfere with medications, but laws don't require that they carry drug-interaction warnings. One example: There is some evidence that ginkgo biloba acts as a blood thinner and may interfere with blood-pressure medications. Your pharmacist can give you recommendations based on your current medications.

• Pay attention to quality. Look for ConsumerLab.com–certified vitamins or supplements, or those bearing either the U.S. Pharmacopoeia's USP Verified Dietary Supplement or the NSF Certified Dietary Supplement seal. These verify that a product is free of contaminants, that it delivers what its label claims, and that the manufacturers comply with the FDA's Good Manufacturing Practices.