When the University of Hong Kong released the results of a study into the effectiveness of acupuncture in treating depression recently, it wasn't the fact that 19.4 per cent of patients reported an improvement in their symptoms that was surprising.
The surprise was that 8.8 per cent of the patients in the study showed an improvement from so-called placebo acupuncture, which used needles that look like the real thing but don't do what real ones do.
Patients' health, it turns out, can improve simply because of the expectation of improvement from receiving medical attention. In other words: the placebo effect is about a lot more than sugar pills.
'The placebo effect is complicated; we don't know how much it's related to expectation and how much to biochemical effects,' says one of the men behind the HKU study, Dr Roger Ng Man-kin, chief of service in the department of psychiatry at Kowloon Hospital.
What's more, Ng says, expectation and medicine aren't mutually exclusive: 'If you have hope about something and then expose the brain to a scan, you'll see changes. Adjusting your mind activity can result in changes to the brain. It's hard to separate physical and mental effects, because they both cause activity in the brain.
'The placebo effect is even more prominent in providing psychotherapy. There's quite a bit of expectation and quite a bit of support that are part and parcel of the treatment.'