How do they test placebos?

I’d be surprised if no one has asked Cecil this, but I can find nothing on it. How do they test placebos? How are they sure that, say, a sugar pill, will have no effect on the condition they’re investigating? They can’t test it against a placebo, of course. So what do they do?

They could test it against a different placebo. One could be a ‘sugar pill’ and another could be made from whatever is commonly used as a filler/binder.

ETA, the wiki page for placebos specifically mentions “Non-inert ingredients of the placebo medication having an unintended physical effect” as a potential issue to keep in mind.

Well, since this a forum about OG straight dope columns and staff reports, here’s one that directly bears on the OP

Which is a detailed analysis of placebo/nocebo effect, and even an additional study that indicates that non-of-the-above could apply.

The study is entitled “Is the Placebo Powerless? — An Analysis of Clinical Trials Comparing Placebo with No Treatment,” by Danish researchers A. Hrobjartsson and P. C. Gotzsche, New England Journal of Medicine, May 24, 2001. The New York Times summarizes it this way:

The investigators analyzed 114 published studies involving about 7,500 patients with 40 different conditions. The report found no support for the common notion that, in general, about a third of patients will improve if they are given a dummy pill and told it is real.

Instead, the researchers theorize, patients seem to improve after taking placebos because most diseases have uneven courses in which their severity waxes and wanes. In studies in which treatments are compared not just with placebos but also with no treatment at all, they said, participants given no treatment improve at about the same rate as participants given placebos.

About to go out for the evening, or I’d see if there is any follow up to the cited article.

They give one group placebos.

They give the other group placebo placebos.

Also, the challenge of testing placebo blockers (perhaps akin to the subject of the column):

Boy, am I glad I asked this question. Or, do I just think I’m glad I asked this question?

You don’t need to test the placebo if you make it out of stuff you are likely to get much more of in your diet.

If you want to be 100% sure your placebo will have zero physical effect on a person just use something homeopathic.

But remember what happened to Edgar Allan Poe’s friend: “The homeopathists did not give him little enough physic, and what little they did give him he hesitated to take. So in the end he grew worse, and at length died.”

That is the suxxor.