Sonntag, 29. Mai 2016

Placebo-Effekt: Double-Blind vs. Double-Blind

I am currently reading Daniel - Moerman’s “Meaning, medicine and the ‘placebo effect'. As well as containing many interesting asides, the book discusses what is at the heart of the so-called placebo effect: patients’ response to the meaning of their treatment. Moerman calls this the ‘meaning response’. This response to meaning explains why two inert pills produce more cures than one inert pill, and why inert injections are even more effective (because “everybody knows” that injections are more powerful than pills). But importantly, it is possible to show that doctors are as important in producing the meaning response as patients. Gracely et al (1985) looked at the effect of placebo on pain in patients having their wisdom teeth extracted. The study was set up as a standard double-blind (neither the doctor nor the patient knows if the patient is getting a real medicine or an inert placebo), with the possibilities being a placebo, fentanyl (which usually reduces pain) and naloxone (which usually blocks reduction in pain, so could be expected to increase the pain of the procedure). The twist was that for the first half of the experiment the doctors, but not the patients, were told that a supply problem meant that no patient would be getting the pain-relieving fentanyl. In the second half the doctors were told that the problem had been resolved, so that now the patients might receive fentanyl. By comparing levels of patient pain in the placebo condition is possible to gauge the effect of doctor expectations on the meaning response of the patients. In this condition patients are all receiving inert substances, and they all ‘know’ the same thing: they might receive a placebo, pain-relief or ‘pain-enhancement’. The doctors don’t tell them about the supply problem and, for that matter, they don’t know themselves for definite what the patient is given. The only difference is that for the patients in the first half, the doctors think they know that pain-relief is not a possibility, whereas in the second half it is.
- The meaning response (Tom Stafford, MindHacks, 05.06.2008)

siehe auch:

Moerman,  Meaning, medicine and the ‘placebo effect' (Leseprobe, U.S. Government system, PDF)
- Specifying the non-specific factors underlying opioid analgesia: Expectancy, attention, and affect (Atlas et al., National Institutes of Health, final edited form: Psychopharmacology (Berl)., März 2014)