I found this question on Quora.
Here’s my answer:
Placebos “can work for conditions that are defined by ‘self-observation’ symptoms like pain, nausea, or fatigue” according to Harvard Medical School Dr. Ted J. Kaptchuk.
His study on patients with irritable bowel syndrome showed improvements even when they were told that the medicine was a placebo.
Since placebos are completely safe, the best way to find out what they can do is to try them out on yourself. Perhaps you can take a Tic Tac and run a little further on your morning jog. Or you can use a glass of water to make you more confident when talking to your boss.
Do not use placebos to treat that weird rash though. Get a doctor to look at that.