system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What happens if you give someone real medicine, but tell them it's a placebo?

Is it possible that real medicine could be ineffective if the patient believes it's a placebo?

Edit - The situation is an elderly relative(81 years) suffering from cancer, who believes his doctors are trying to "kill him"(some of the best doctors in the city). Could his cancer medication be rendered less effective by his belief that the medicine is harmful?
gpt
It can be less effective, yes. 

I've recently read a study that showed patients still received positive benefit from placebos even knowing it's a placebo.

So in other words, the placebo effect can be very potent.