Nocebo effect

The nocebo effect is when someone expects something to go wrong, then it does. It's like the opposite of the placebo effect which is when someone expects something to help, then it does. The nocebo effect happens when somebody expects the worst and that is what happens. For example, someone might be afraid they're going to get a headache if they take a certain medicine, and then they do get a headache even though the medicine isn't actually giving them one.