No drug in the pill.
So who stops the pain?

The full narration of the video.

Swallow a sugar pill, and the pain really can ease, and you're not faking it. A sugar pill looks like medicine, but there's no drug inside. Yet if people think they've taken a painkiller, the pain often really does ease a little. So if the pill does nothing, who is stopping the pain? First, where pain comes from. You bump your knee, but the knee can't feel pain by itself. It fires off a string of signals up your nerves, and only when they reach the brain do you feel it.

Picture those signals as a line of cars. They leave the knee, take the highway of the spinal cord, and drive into the city of the brain. The more cars get into the city, the more it hurts. On that road there's a junction, and the brain controls it. The brain can send traffic police down to stop cars there. More cars stopped, fewer cars in the city, and the pain eases. Their tool is a painkiller the body makes itself, in the same family as morphine. Could a placebo simply be calling in the police?

One experiment set out to check. People who had just had teeth pulled got a shot of salt water they thought was a painkiller. For some of them, the pain really did ease. Then the researchers gave them a shot of naloxone. It switches off the body's own painkillers, like pulling the police off the road. And the people whose pain had eased felt it come back. Pain returning when the police leave means police really were on duty. A placebo isn't all imagination: the brain really releases its own painkillers. Later, brain scans showed the pain areas lighting up less, too.

Now the real names. This top-down way of stopping pain is called descending pain modulation. The painkillers the police use are endorphins and their relatives. So what makes the brain send them? Expectation. You've taken pills before, and they've helped. Handed another one, the brain bets the pain will ease and sends the police out early. So the effect varies, and on average it's modest. It mostly changes how pain feels, and a sugar pill can't heal the injury itself.

Stranger still, one trial told people with back pain straight out: this is a sugar pill, no drug inside. They took it for three weeks, and their pain still eased a bit. When it really hurts, though, ask a doctor what to take. Have you ever swallowed a pill and felt better before it could possibly have kicked in?