The supplement aisle at the drug store is lined with products that promise to prevent illness, improve energy, boost metabolism, even brighten your skin. You probably already know these capsules aren’t necessarily silver bullets to perfect health. (Whatever benefits your multivitamin or Omega-3 supplements offer, you still have to exercise and eat right, for example.) But you do expect them to be safe to swallow, at the very least.

Sadly, a new study in the Journal of the American Medical Association suggests otherwise. After analyzing supplements that had been recalled by the FDA for containing banned substances—such as steroids or powerful prescription medications like Viagra and Prozac—researchers found that roughly two-thirds of the tainted products were back on store shelves with the same illicit ingredients at least six months later.

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Because supplement makers are subject to little regulatory oversight from the U.S. Food & Drug Administration, they aren’t required to prove a product’s safety (or efficacy) before it goes to market. And as this study shows, some fail at accurately providing the most basic safety information.

That said, the supplement industry is vast; Americans are expected to spend $32.4 billion on vitamins and dietary supplements in 2014, according to a Euromonitor International report. And there are reputable, safe supplement-makers out there.

Our buyer’s guide can help you avoid sketchy ingredients and choose the most established, trusted brands.

Be wary of certain types of pills
Namely exercise, weight-loss, and sexual-enhancement supplements. The products analyzed in the JAMA study fell into these three categories. Several of the weight-loss supplements actually contained an amphetamine-like drug called sibutramine, which is banned in the U.S., Asia, and Europe.

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Shop selectively
Big-chain drugstores, pharmacies, and supplement stores like GNC or the Vitamin Shoppe may act faster to pull recalled items.

Don’t bargain-hunt
A University of Minnesota analysis found that for six types of herbal products, the more expensive the supplement was, the more likely it was that the recommended dosage would be consistent with established standards.

Steer clear of supplements made in China
Lack of regulation and poor manufacturing practices in China mean their goods may be more likely to be contaminated with substances like lead.

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Check for a USP Verified Mark
It means that the nonprofit US Pharmacopeia has verified that a product contains the ingredients on the label in the amounts specified and doesn’t contain unacceptable levels of contaminants.

Do research at reputable sites
You can read supplement fact sheets from National Institutes of Health Office of Dietary Supplements to get all the info you need on everything from the recommended daily amount (RDA) to the latest on the health benefits of a certain supplement. It’s also a good idea to stay on top of warnings or recall alerts from the FDA. When you’re ready to buy, the USP website has a store directory and list of all the participating supplement companies if you want to check before you head to the store.

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Consult the experts
Namely, the store pharmacist and your doctor. The former can alert you to any potential adverse events or drug interactions, and your doc can advise you on which supplements are safe and effective.

Skip dubious ingredients
These four have been linked to serious side effects, and aren’t worth the risk.
1. Kava. It has been reported to cause liver damage.
2. Bitter orange. It contains the chemical syndephrine, which has been linked to heart attacks and strokes in healthy people when taken alone or combined with caffeine.
3. Contaminated L-tryptophan. It’s associated with neurotoxic reactions.
4. Chromium. When overused, it’s been linked to anemia—even kidney failure.

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With additional reporting by Hallie Levine

This article originally appeared on Health.com.