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By Lauren F. Friedman

Psychology Today Magazine

Imagine you have a choice between two medications. One is advertised as “natural,” while the other is a conventional pharmaceutical.

Would you prefer one to the other, or would you be indifferent? What if you learned that the two substances are chemically identical, with the same success rates and side effects? Would you consider changing your mind?

Opinions about natural medicine can vary widely among cultures and individuals, but when this thought experiment was presented to a diverse sample of Philadelphians, 58 percent expressed an immediate preference for the natural remedy. Even when those participants were told that the medications were chemically identical, only 18 percent of them adjusted their answer to conventional or indifferent.

If two substances are functionally indistinguishable, with the very same outcomes – what explains the persistent preference for one over the other, just because it’s called “natural?” Logically, the two products would seem to be interchangeable, but when we make a decision based on limited information, logic doesn’t have much to do with it.

“The way we perceive risk is not just about the facts; it’s about how the facts feel,” said David Ropeik, author of “How Risky Is It, Really?” “Natural risks worry us less.”

A “natural preference” bias is well established when it comes to food and persists even when the arguments people use to justify it become moot. Our trust in the natural world may be elemental, something that cuts deeper than deliberation.

The biophilia hypothesis, introduced by Harvard biologist E.O. Wilson, posits that humans feel an affinity for other living things.

“We don’t see nature as out to exploit or harm us,” says psychologist Paul Slovic of Decision Research.

Paul Rozin, the University of Pennsylvania psychologist who led the Philadelphia experiment, has found that when people free associate with the concept of “natural,” almost all of their associations are positive.

Once the image of safety and purity has set in, it’s hard to shake. Even when an herbal medicine yields adverse results, it’s associated with weaker feelings of anger and regret than when the very same damage is done by a synthetic, Princeton psychologist Eldar Shafir has shown. Meanwhile, if an herbal remedy and a prescription both lead to the same positive outcome, subjects tend to say that the herbal option was more effective.

The mostly favorable impressions of herbal treatments suggest that in the U.S., natural medicine is not going away. All told, we spend about $22 billion each year on natural products, and herbal medicine has been the fastest-growing category.

Of course, perceived safety and actual safety are different beasts.

“Although herbs are often perceived as ‘natural’ and therefore safe, many different side-effects have been reported, owing to active ingredients, contaminants, or interactions with drugs,” noted a review in the Journal of Internal Medicine. Yet a study of Italian women found that 72 percent of those who used herbal products never told their physicians, largely because they perceived the therapies as risk-free and assumed their doctors wouldn’t know much about the products or care.

“People are forced to trust a system that they don’t understand,” says Baruch Fischhoff, a decision scientist at Carnegie Mellon and a former chair of the FDA’s Risk Communication Advisory Committee. “It’s not a consumer failure; it’s a market failure.”