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Head to the drugstore to pick up medications for allergies, insomnia or migraines, and homeopathic remedies may be sitting right next to conventional over-the-counter drugs. But there are important differences between the two. OTC drugs contain active ingredients that the Food and Drug Administration has reviewed for safety and effectiveness. Homeopathics are sold without those reviews.

Homeopathy, a centuries-old form of medicine, is based on the theory that “like cures like.” So an allergy remedy may contain Allium cepa (red onion), which proponents claim has a beneficial effect because onions cause irritated eyes and a runny nose, just as allergies do. Another tenet: The more diluted the “active” ingredient, the greater its benefit. In fact, by definition homeopathic remedies may be so diluted that the helpful ingredient is no longer even detectable.

According to Marvin M. Lipman, Consumer Reports’ chief medical adviser, these tenets don’t make much sense. “The concepts behind homeopathy are irrational and defy our understanding of the laws of nature,” he says. But sales are surging. U.S. consumers spent about $1.2 billion on homeopathic drugs in 2014, according to the Nutrition Business Journal. Here’s what you need to know before you buy.

Does homeopathy work?

Proponents say that homeopathy can treat many conditions, including asthma and heart disease.

Yet after reviewing 176 studies, the National Health and Medical Research Council in Australia this year found that homeopathics worked no better than placebos, concluding that “there are no health conditions for which there is reliable evidence that homeopathy is effective.”

Why, then, are they so popular? “Some trials done 20 years ago seemed promising,” says Adriane Fugh-Berman, an expert in botanical medicine and an associate professor of pharmacology at the Georgetown University Medical Center. But Fugh-Berman says more recent and scientifically rigorous trials don’t support homeopathy.

In an email to Consumer Reports, Alissa Gould, a spokeswoman for the American Association of Homeopathic Pharmacists, cites a “significant body of evidence that supports the effectiveness of homeopathy,” including a large 2011 report by German researchers. But after evaluating many reliable studies, including comprehensive, independent reviews of the research, Consumer Reports’ medical experts conclude that homeopathic preparations are no more effective than a placebo.

Regulating homeopathics

The FDA classifies homeopathics as drugs. As with other drugs, manufacturers must include a list of ingredients, instructions and at least one medical condition their product is supposed to treat. Those that are said to treat a serious condition, such as cancer, must be sold by prescription.

But unlike with prescription drugs and the active ingredients in OTC products, which are reviewed for safety and effectiveness before they’re made available to the public, the FDA doesn’t require makers of homeopathics to submit evidence that their products work or are safe to use. And the agency doesn’t routinely evaluate them. Instead, it requires that they contain ingredients listed in a database managed by the nongovernmental Homeopathic Pharmacopoeia Convention of the United States.

But that could change. Homeopathy’s rise in popularity is prompting the FDA to examine how the products are evaluated and the Federal Trade Commission to investigate manufacturers’ marketing claims. In September, the FTC held a workshop to evaluate advertising for over-the-counter homeopathic products. The workshop brought together a variety of stakeholders, including medical professionals, industry representatives, consumer advocates and government regulators. The FTC also invited the public to submit comments on homeopathic marketing.

Confusing packaging

Some homeopathics look similar to conventional OTC medicines. And because they’re often placed side by side on drugstore shelves, it’s easy for consumers to choose one unintentionally.

“It’s misleading and indirectly harmful,” Lipman says. “If you need a decongestant and buy a homeopathic product instead of a real medication, you won’t get relief. Consumers should read labels carefully.”

Copyright 2015. Consumers Union of United States Inc.

For further guidance, go to www.ConsumerReports.org/Health, where more detailed information, including CR’s ratings of prescription drugs, treatments, hospitals and healthy-living products, is available to subscribers.