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ost of the time, it’s easy to be in the placebo group of a clinical trial: no side effects, minimal annoyance, and you may even get paid for it. (Though, of course, for people hoping the therapy will treat their illness, it’s often disappointing to learn they’d been getting a sugar pill the whole time.)

But in studies testing surgical procedures, getting a placebo can mean going under the knife. So-called sham surgeries are a kind of extreme placebo, where patients undergo all the rituals and scars of a surgical procedure except for the part meant to help.

These patients benefit surprisingly often: In about three-quarters of sham-controlled studies, there’s some improvement, according to a 2014 review. And they actually benefited just as much as those who got the actual intervention a whopping half the time. And therein lies perhaps the greatest contribution of sham surgeries: helping shine light on popular surgical interventions that might be shams themselves.

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Here are some of the wilder ways that patients have been tricked into thinking they had real surgery, all in the interest of advancing science:

1. Incisions in their chests

In the 1940s and ’50s, doctors thought they had found an amazing new way to treat the chest pain caused by a shortage of blood flow to the heart: cut into patients’ chests and tie up two of their arteries. But then in 1959, a landmark study put the procedure to the test. In the placebo group, sedated patients got the incisions but no knotted arteries. The upshot: Patients who got the sham surgery fared no worse than those who got the actual intervention. That helped the ineffective procedure fall out of favor.

2. The smell of cement

Patients getting a sham procedure must really be convinced that they’re getting the actual surgery — and in one 2009 trial, researchers took a particularly elaborate approach to ensuring the ruse. The trial was testing a pain relief tactic for osteoporosis, in which medical cement is used to seal up cracks in the spine. Patients in the placebo group didn’t get actual injections, but researchers applied pressure to their backs and prepared the cement mixture so patients would smell it. That study concluded that the cement sniffers fared just as well as those who got the real thing, a finding that helped discredit the procedure.

3. Holes in their skulls

Can Parkinson’s disease be treated by implanting neural cells in the brain? For patients in the handful of those trials run over the past 15 years, being in the placebo group typically means getting small holes drilled in their skulls. (Don’t worry, their brains didn’t get cut.) Patients who’ve gotten these sham surgeries have typically fared just as well as those who got the real thing, helping show that the science of treating Parkinson’s in this way is still in its infancy.

4. The sounds of surgery

After people get their gallbladders removed, they sometimes experience pain in that region. In certain cases, that pain is treated by another small surgery in the region. In a 2000 study testing the efficacy of that procedure, patients in the placebo group got a tube inserted into their small intestine and then researchers made all the typical surgical “noises” — but none of the cutting. Turns out, that didn’t work as well as the real thing.

5. Deflated balloons in their stomachs

For morbidly obese patients, balloons inflated inside the stomach have been touted as a solution to make them feel fuller and eat less. In one 2007 study putting this intervention to the test, the placebo group got deflated balloons inserted through their mouth down into their stomach. That study found that the inflated balloon made patients feel more full in the short term.

6. The sensation of a needle

Acupuncture provides an intriguing challenge for the clinical trial designer: how do you simulate the insertion of needles without, well, inserting them? One widely-used solution: blunt-tipped needles that retract into a hollow shaft when they’re pressed into the skin. Trials that have used these needles for the placebo group have often found that patients tricked this way fare just as well as those who get the real thing. That’s added to the evidence suggesting that a powerful placebo effect is at play in patients who feel pain relief from acupuncture.

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