There is evidence that placebos can treat pain and affect mood and immune response.

The endocannabinoid system (ECS) has been shown to be involved in delivering placebo-mediated analgesia.

The ECS appears to play a central role in creating homeostasis throughout the body.

The placebo effect has been part of medical conversation since the late 1700s, when an English physician named Dr. Alexander Sutherland coined the term to describe a doctor with an especially reassuring bedside manner. Today, the concept plays a central role in how we test new drugs: to prove a medication actually works, researchers have to compare it against a "dummy" pill or injection—something inert, with no active ingredient. Neither the patient nor the doctor is told which one the patient is getting, a setup called a double-blind, placebo-controlled trial. This precaution exists because up to 40% of patients feel real, measurable benefits from a completely inactive treatment, simply because they believe it's the real thing.

When Belief Changes the Body

What's fascinating—and a little unsettling—is that over three centuries of medicine, we've learned that believing a treatment will help can cause the body to respond as if that treatment (proven or not) actually did. Studies have shown that a plain saltwater injection can ease pain, and a sugar pill can lower blood pressure.

I saw this firsthand during my medical residency. At the time, there was a common (and, I now think, troubling) practice: if a patient came in reporting pain and staff suspected they were exaggerating to get narcotics, we'd give them a shot of saline instead. If their pain went away, we took that as proof they hadn't really been in pain—they were just drug-seeking. Looking back after more than 40 years in medicine, I'm no longer confident that conclusion was right, and I've come to have real concerns........

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