Since Michael Phelps was spotted spotted at the Rio de Janeiro Olympic Games, Google searches for cupping have skyrocketed to levels not seen since Jennifer Aniston walked the red carpet with visible cupping circles. And while we all know it’s usually not great to take health advice from mere celebrities, Olympic athletes have got to know what they’re talking about when it comes to recovery tricks. Right?

Cupping is an ancient Chinese healing practice in which a vacuum is applied to the skin via cups, presumably to alleviate sore muscles and aid in recovery. It causes the now-famous circles that are, for all intents and purposes, large hickeys.

But does it work? That depends on what you mean by “work.” People who do it definitely believe in it, but the most remarkable thing about cupping is how powerful it shows the placebo effect can be.

Many have reported that the medical literature on cupping is inconclusive. That strongly suggests that it doesn’t actually work. In fact, the literature is a bit of a hot mess. Almost every study of cupping has been highly biased, because neither the patient nor the doctors were blinded to the intervention. People believe cupping works, so when it happens to them, they report feeling better. You can’t exactly fake cupping—everyone knows when it happens. This makes a good control group almost impossible to come by. Unfortunately, this also renders a study’s conclusion largely uninterpretable. Some of the studies were poorly designed with patients compared to improper control groups. In several studies, patients were randomized to either cupping or a waitlist. People don’t exactly like waitlists.

Yes, there have been a couple of meta-analyses that pool together all the data we have on cupping, which have concluded that it is possibly slightly effective. Unfortunately, when you pool together a bunch of biased studies, the results are also probably biased. In more rigorous meta-analyses, such as those performed by organizations like the Cochrane Collaboration, studies that are highly biased are usually excluded from consideration. What’s more is that even these unblinded studies haven’t shown that cupping firmly works—which is unusual because unblinded studies almost always heavily favor the intervention.

What the studies do seem to suggest, however, is that cupping is probably safe. I emphasize probably because cupping has been implicated in burns, and rarely, in serious vascular injury and even infections causing sepsis, adverse effects that have not appeared in the mainstream press and that experts I spoke to appeared to be surprised to learn.

What would make cupping work, biologically speaking? The main hypothesis is that cupping increases blood flow to a sore area, alerting the body that a certain area needs attention. This is accomplished by the suction, which bursts capillaries apart causing blood to spill out into the surrounding soft tissue—resulting in that now-famous hickeylike bruise. The burst capillaries jumpstart the body’s natural inflammation cascade. Wait, but why would athletes want to incite inflammation? All first-year medical students are taught that inflammation is “rubor, calor, tumor, dolor.” That’s redness, heat, swelling, and pain. We know cupping causes redness. We also know it causes heat. (Burns are a known risk . ) We know it causes swelling. (All bruises swell.) So why would cupping not cause pain? The answer is that it probably does. But just like massage, that pain can either feel great or hurt. It depends on the practitioner and the injury.

Is inflammation what athletes want when they are stiff? Maybe in the long-term. Inflammation is indeed the body’s adaptive response to minor injuries and is how we heal. But for immediate peak performance, increasing inflammation doesn’t make sense.

In what sense, I asked, is cupping any different than say, getting a bruise after being hit with a blunt object like a baseball bat?

“It isn’t,” says Dr. Houman Danesh, assistant professor of anesthesiology and rehabilitative medicine at the Icahn School of Medicine at Mount Sinai Hospital in New York. “But it’s more like getting hit with a stick,” he admits.

So why does cupping help athletes, as Danesh thinks it does? It may be because some pain can be perceived as positive, and even pleasurable in the right circumstances. Injury incites the body to release chemicals that help dull pain—that’s what some people get from self-harm. Another explanation is that cupping separates planes of muscles that have been rendered stiff by overuse. If so, the massagelike property of cupping might improve the body’s clearance of lactic acid by increasing local blood flow, though this explanation means that there’s no reason cupping would be more effective than massage.

“It’s all speculation,” says Dr. David Shurtleff, deputy director of the National Institutes of Health’s National Center for Complementary and Integrative Health. “There have been no studies that have looked at muscle blood flow and activity before and after cupping.” As for a real understanding for how cupping might work? “My read of literature is that it is just not there,” says Shurtleff.

There are many treatments that work despite our poor underlying understandings and others that don’t work as well as we think they should in theory. But when it comes to cupping, the data seem to indicate that we’re dealing with a very exaggerated case of the placebo effect. People think it works so strongly that, in effect, it does.

In fact, even cupping researchers and other experts have come out and admitted this. Leonid Kalichman, a researcher at Ben-Gurion University of the Negev in Israel, told the New York Times that “[a] placebo effect is present in all treatments, and I am sure that it is substantial in the case of cupping as well.”

But whenever a physician says that a therapy works by the placebo effect, that is another way of saying that it doesn’t work at all. And while the placebo effect can be incredibly strong, is it strong enough to overcome a self-induced mild injury? That is an idea that, to my knowledge, has never been tested.

In medicine, we like to say that plural of an anecdote is not data. And while athletes seem to like cupping, that does not mean it is actually beneficial. So, until high-quality data emerges, it’s safe to assume that cupping, like other fads, is another expensive placebo.

Disclaimer: The opinions expressed in this article are solely those of the author and do not reflect the views and opinions of Brigham and Women’s Hospital.

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