The placebo is the most tested product in human history (because placebos are used in clinical trials of new drugs).

While it's important to distinguish between an open-label placebo (like Placebex) and a blind placebo, these papers offer a wide sampling of the research on inert pills:

💊  A 1990 study in Headache studying placebos and NSAIDs (eg naproxen) f

💊 A 2016 study in The World Journal of Gastroenterology studied placebos and probiotics.

💊 A 2014 letter in The Lancet describes placebos and acetaminophen.

💊 A 2018 study in Obesity Surgery describes the use of placebos and IV tylenol.

💊 A 2007 study in the Journal of Psychiatric Research studied placebos and  Prozac (fluoxetine).

And here are 1,000 more papers that feature placebo-controlled trials.