The mind is a powerful medicine. Given an ineffective treatment, patients can experience real health improvements by simply believing that the treatment works—the placebo effect. But this blissful delusion has a dark side: when a harmless placebo becomes effective, it becomes harmful, too, causing side-effects seen in actual therapies. In a new study exploring this mysterious “nocebo effect,” researchers pinpoint regions of the brain that seem to be behind phantom injuries. They also assess factors—framing and price—that can increase the potency of the effect. These may be critical to designing and assessing clinical practices and trial results, they argue.