Jo Marchant is a science journalist and the author of “Cure: A Journey Into the Science of Mind Over Body.”

I once interviewed a woman who’d fractured her spine. For months, she was laid up, barely able to walk. Finally, her doctor recommended an experimental treatment. She agreed to try it; afterward her pain melted away. A decade later, she’s still playing golf. In truth, she didn’t get the experimental spine treatment. She was given a placebo. The “placebo effect” is a phenomenon in medicine whereby patients feel better without the use of drugs. Although scientists have been studying placebos for decades, there are still a lot of misconceptions about how and why they work. Here are the most common.

1. The placebo effect is all in the mind.

A significant proportion of patients feel better after taking placebos, but many scientists claim that this improvement is totally mental — that patients only think they feel better. Prominent doctors have called the placebo effect a “myth” or the “beer goggles of medicine.”

In reality, placebo treatments can cause measurable, biological changes similar to those triggered by drugs. Studies show that depressed patients on placebos experience increased activity in their prefrontal cortex, which eases their symptoms. Other research has shown that in patients with Parkinson’s disease, placebos trigger a flood of the neurotransmitter dopamine, just as their drugs do. And taking a placebo painkiller dampens pain-related activity in the brain and spinal cord and causes the release of pain-relieving endorphins.

2. Placebos work only if patients think they’re real.

Expecting to feel better is a key ingredient in placebo responses, so it might follow that if a patient knows a treatment is fake, it won’t have any effect. Physicians and researchers have questioned the ethics of placebo use, suggesting that it requires doctors to willfully deceive their patients.

Over the past few years, however, scientists have found that this isn’t true. Honest placebos work, too. In one trial, patients with irritable bowel syndrome were told that they were taking a placebo, yet they still experienced significant relief from their symptoms compared with patients who got no treatment. Researchers have found the same effect for depression, migraines and ADHD.

There are several possible explanations. Some research shows that patients learn to associate taking a pill with a particular physiological response, so when they subsequently take a placebo, their bodies automatically mimic that response — a phenomenon known as conditioning. There’s also evidence that simply being cared for in a trial — even if patients know that a treatment is fake — eases anxiety and helps them feel that their conditions will improve.

3. Neurotic, suggestible people are more likely to respond to placebos.

Doctors once took a very patronizing view of placebos. A 1954 article in the Lancet, for example, advocated placebos as a means to comfort “unintelligent or inadequate patients.” That belief — that placebo responders are pliable, suggestible souls who simply wish to “please the investigator” — persists today.

Recent studies, however, suggest that anyone can respond to a placebo. Crucial factors include patients’ attitudes toward a particular treatment, their previous experiences (whether, for example, they’ve responded well to a particular drug) and the information they’re given about a treatment. Genes also play a role.

About a quarter of the variation does seem to depend on personality. It’s not neurotic people who see benefits, though, but rather those who are optimistic, altruistic, resilient and straightforward. Scientists think this is because these personality types tend to be more engaged with their treatment and have more positive expectations for it. Neurotic and hostile people are least likely to respond.

4. You have to take a placebo to get a placebo effect.

The placebo effect is commonly defined as what happens when a patient takes a placebo, or as the benefit experienced by someone in the placebo arm of a clinical trial.

It’s true that placebos won’t shrink a tumor, cure an infection or replace insulin in someone with diabetes. But many “real” medical treatments — particularly those that modify symptoms like pain, fatigue, nausea or depression — rely on the placebo effect. Common opioid painkillers such as Tramadol are about a third less effective if we don’t know we’re taking them, for example. In a study that followed 459 migraine attacks, the placebo effect accounted for 60 percent of the benefit of the painkiller Maxalt. Meanwhile, in mild to moderate cases of depression, the placebo effect is thought to account for almost all of the benefits of the drugs patients take.

5. Drugs are always more effective than placebos.

An oft-cited 2001 analysis compared patients given placebos with those given no treatment in 130 trials. The researchers found little evidence that the placebos had powerful clinical effects. “Outside the setting of clinical trials, there is no justification for the use of placebos,” they concluded.

But that analysis lumped many different conditions together (from Alzheimer’s disease and anemia to marital discord and problems reaching orgasm). And it incorporated trials in which the drugs being tested didn’t work, either. A rigorous, more recent study of 152 trials found that placebo effects are often about the same as drug effects.

Of course, when patients take an active drug, they benefit from both the drug and the placebo effect. But medication can also do harm; 16,000 Americans die from overdoses of prescription painkillers each year, for example. And in some cases — when people respond particularly well to placebos, or when drugs aren’t very effective or have significant downsides — patients might do better taking a placebo. A 2007 trial of more than 1,000 patients with back pain found no difference in benefits between real and sham acupuncture, a placebo intervention in which needles don’t deeply penetrate the skin. But both groups did significantly better than patients given conventional treatment (a combination of drugs, physiotherapy and exercise). For conditions like chronic pain, for which drugs aren’t especially effective, these placebo effects mean that patients can actually do better with alternative therapies than with conventional drugs, as this trial shows.

What’s more, neuroscientists are finding that beliefs and expectations about treatment influence the brain in ways drugs don’t. For example, taking a placebo can trigger areas in the prefrontal cortex that are involved in motivation and decision-making. This goes beyond easing symptoms to influence how patients cope with those symptoms: how much their conditions distress them, and whether they mope at home or go out and enjoy life. While drug effects last only as long as patients keep popping pills, these changes rely on their inner resources, which they can access at any time.

Twitter: @JoMarchant

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