After visiting the Roman Catholic shrine in Lourdes, upon seeing the collection of discarded crutches that testified to the shrine’s curative powers, a traveling companion remarked to the writer Anatole France, “One wooden leg would be more to the point.” This anecdote is a favorite of skeptics who disbelieve stories of faith healing. Yet such faith persists. In September, 2009, for instance, Pope Benedict XVI approved the claim that a Boston man was “miraculously cured” of back pain after praying to Cardinal John Henry Newman, a British theologian who died in 1890.

Are those who seek faith healing deluded? Not entirely. Although no amount of faith can regenerate a lost limb, faith can indeed help a person overcome crippling pain. The natural brain mechanisms that allow this to occur are increasingly understood. Believing in a Higher Power—even a fictional one—can cure ills amenable to the placebo response. Yet with the right approach, even skeptics can take advantage of placebo mechanisms.

Contrary to the notion that a placebo is “nothing,” placebos have been shown to have a significant effect on pain, depression, and Parkinson’s disease, all of which are conditions of the brain’s motivational circuitry. Placebo effects have been reported but are less well-established in the treatment of other conditions such as alcoholism. Twelve-step programs call for belief in a Higher Power, but are liberal as to what it can be; as Nicholas Grant Boeving notes, even a doorknob can fit the bill. This Higher Power is clearly some kind of fictive device that gets the action rolling, like the statue that serves as a “MacGuffin” in The Maltese Falcon, or like a placebo.

The best-understood placebo response is the one that relieves pain. This response is a feature of the brain’s “reward system,” the part of the nervous system that drives us to achieve goals. Pain is a signal that interrupts this system and tells us to stop and pay attention. Both pain and reward make use of a common currency—the body’s internal opioids—that both relieve pain and induce pleasure. Another aspect of the reward system is habits, which serve as a kind of an automatic pilot for actions proven so rewarding we don’t need to analyze them anymore.

Narcotics, in fact, hijack the reward system by mimicking the body’s natural opioids. An addiction is a very strong habit. When one is addicted, one can’t easily choose to do otherwise. Thus, it’s wiser to think of addiction as a disease rather than a moral failing. Yet addictions are less hard-wired than genetic disorders. To use a technical term, addictions are the result of “neuroplastic” changes to the brain’s wiring that are enduring but not necessarily impossible to reverse.

In the 1970s, when internal opioids were first identified, the neurologist Howard Fields and colleagues at the University of California, San Francisco showed that the placebo effect on pain disappeared when patients received an opioid-blocking drug. In a recent lecture at Brigham and Women’s Hospital in Boston, Fields, slim and with a full head of gray hair, spoke about the interplay between pleasure and pain. “A placebo actually is the anticipation of reward, because the anticipation of pain relief is a reward,” Fields said. The amount of pain we feel is altered by computations in the reward system a half-second before pain reaches consciousness. “There’s a big opioid release in the nucleus accumbens with the anticipation of reward,” Fields said. “It’s biasing the system.”

According to Italian researcher Fabrizio Benedetti, injecting a placebo saline solution in full view of the patient has the same punch as providing 6–8 mg of morphine—a significant dose—through an IV line without the patient’s knowledge. Even “real” drugs, such as narcotics, are amplified by the placebo response. “When you administer an agent or a treatment openly, the effect that it has is doubled—the effect of the active treatment and then the effect of the expectation,” University of Michigan psychiatrist Jon-Kar Zubieta told me. “Both come together. Morphine has a huge effect like that.”

Zubieta’s research shows that when people respond to placebos, elevated levels of internal opioids spread from the reward system to brain areas that regulate pain. So although faith can’t regenerate limbs, there’s a clear biological mechanism to go with the anecdotal and statistical evidence that faith reduces pain.

The healing by prayer of the future founder of Christian Science, Mary Baker Eddy, bears evidence of this type of cure. Immobilized after a fall on an icy sidewalk in Lynn, Mass. in February, 1866, she was inspired by an account of Jesus healing the infirm to rise from her sickbed and walk.

It may seem puzzling that faith can have a long-lasting healing effect. Elevated moods do not last forever. However, faith can permanently relieve pain when the pain is itself the product of false beliefs. A nocebo—sometimes called the placebo’s “evil twin”—is an inert substance or procedure that makes a person feel worse via the power of suggestion. Ironically, when participants in clinical trials receive placebos, they sometimes come down with the side effects listed on the warning label of the real pharmaceutical. Among the recorded “side effects” of placebos are burning and flushing, chills, diarrhea, drowsiness, dry mouth, insomnia, nausea and numbness.

Jon-Kar Zubieta has found that subjects who experience elevated pain due to a nocebo response have reduced opioid transmission in their reward system. That is, just as positive expectations raise internal opioid levels, pessimism lowers them.

When nervous people like Mary Baker Eddy anticipate the worst, their negative expectations can become a self-fulfilling and enduring prophecy. But when they are inspired by the Bible, a shaman, or even a back surgeon to expect recovery, that shift in expectations can restore them to their natural pain-free state. Faith is a nocebo-buster.

I had my own powerful nocebo experience when I was in my twenties. Over a period of eight years, increasingly intense eyestrain made it difficult for me to work—to the point where I applied to be certified as visually handicapped. I saw eye doctors—including one who suggested it was psychosomatic, a diagnosis I rejected indignantly. Finally, I was referred to an ophthalmology specialist at the University of California, San Francisco Medical School. He told me that my eyes were fine, but that I’d become hypersensitive to minor eye sensations. A thought struck me. My overprotective mother (a graduate of Philip Roth’s Weequahic High School in Newark) had frequently warned me about reading too much, even shrieking, “Stop reading. You’ll be blind by the time you’re thirty.” I was nearing thirty and imagined I was going blind. It was a self-fulfilling prophecy.

My eye pain faded over the next 48 hours, and I was able to function normally again. It felt like a miracle—like I was born again—and if it had happened at Lourdes rather than UCSF, I might be Roman Catholic today. Was it a coincidence that my healing occurred at UCSF, where Howard Fields’ research demonstrated that placebo analgesia was due to internal opioids? No, I suspect the physicians there were in general well-informed about the impact of beliefs on pain.

Modern, secular people may be too sophisticated to believe religious fictions that produce placebo analgesia. However, even highly educated people can hold secular fictions that make life painful, and we can undo those by applying our critical faculties. In a 2000 book, the late Patrick Wall, a leading figure in pain research, wrote that no more that 15 percent of patients who seek treatment for back pain have an identifiable physical condition. “This leaves 85 percent with no apparent cause,” he wrote. Many back specialists now believe a nocebo response is responsible for much unexplained back pain, which also explains why dubious treatments can cure it. For instance, in January 2010, a back specialist wrote in a medical journal that he would continue to inject liquid cement into the spine of certain back-pain patients, even though studies show it provides no more benefit than a sham procedure that mimics it—because both the real and placebo procedures provide long-term pain relief.

Because false expectations can cause physical pain, cognitive behavioral therapy, which aims to dispel false beliefs, can act as anti-nocebo therapy for pain. Timothy Wallace, a clinical psychologist at Spaulding Rehabilitation Hospital in Boston, works with patients to correct their distorted beliefs about pain. “Pain is more than just something going on wrong inside your body,” he told me. “It’s all about expectations and past history and your thinking about pain.”

Ronald Siegel is a psychologist on the clinical faculty of Harvard Medical School and co author of the book Back Sense. With regard to treating back pain, he said that shifting a client’s expectations in a positive direction is a key element whether the treatment is surgery, psychotherapy, or alternative treatments such as chiropractic or acupuncture. “Talking about back pain for the moment—anything that will make a person believe that they have found a successful treatment will be very, very helpful in alleviating pain,” he said. Before trying to psych out pain, however, one should consult a physician to get a correct diagnosis. “You don’t want to psychoanalyze a brain tumor,” Siegel said.

A stumbling block to the use of psychotherapy in the treatment of nocebos is the oversold notion that psychosomatic illness is the result of “secondary gain.” This is the idea that people become sick because they have a desire, perhaps unconscious, to be catered to as an invalid. There is no reason to posit such florid motivations for these illnesses ; negative expectations—perhaps due to an innocent error—can depress opioids and amplify pain. When I related my story to Arthur Barsky, the vice chair for psychiatric research at Brigham and Women’s Hospital in Boston, he downplayed motives of secondary gain in conditions like mine. “For many of these patients, they’re not getting anything out of it. It’s miserable,” he said. “It’s not a way of manipulating other people or getting some gain that you couldn’t get any another way.”

I don’t mean to reduce the balm of religion solely to the placebo response. For instance, the ideas that “things happen for a reason” or that tragedies are “God’s will” are forms of cognitive reappraisal. When we reappraise, prefrontal areas of the brain inhibit pain-related activity in the cingulate cortex. Meditation and mindfulness are being studied in laboratories as ways of reducing suffering. Even religious art and music that inspire, and secular versions of the same, can reduce pain.

The endurance of religion in the modern age may have something to do with its analgesic properties. Those of us who are too skeptical to resort to faith healing can at least debunk our nocebos. We can apply skepticism toward our own bodies, and challenge false beliefs that cause us pain. Nocebos can happen to anyone—in his research, Zubieta has yet to uncover a personality trait that makes someone significantly more susceptible to them. After all, who doesn’t have some false beliefs? Indeed, people who are certain that all their beliefs are true may be the ones most deluded. Faith can work miracles by way of the brain’s reward system. Judicious use of skepticism, when applied to unjustified fears and excessive pessimism, can heal us too.