In another clinical trial, patients were asked whether they considered acupuncture to be an effective therapy in general and what they personally expected from the treatment. Patients with higher expectations about acupuncture experienced larger clinical benefits than those with lower expectations, regardless of their allocation to real or sham groups (Linde et al., 2007).
It did not really matter whether the patients actually received the real or the sham procedure—what mattered was whether they believed in acupuncture and expected a benefit from it.
Kaptchuk et al. (2006) compared two placebo treatments in a clinical trial of 270 patients suffering from arm pain resulting from repetitive use or prolonged static postures. The two placebo treatments were acupuncture with a sham device twice a week for 6 weeks, and a placebo pill once a day for 8 weeks.
The investigators found that the sham device had greater effects than the placebo pill on self-reported pain and severity of symptoms over the entire course of treatment. This suggests that placebo effects depend on the behaviors embedded in medical rituals, which, in turn, may induce different expectations.
The comparison between two placebos is an interesting experimental approach in order to demonstrate real placebo effects and the involvement of different levels of expectations. In fact, if a placebo is inert and does not produce any psychological effect, two different placebos should not differ from each other. Conversely, if the psychological effect of a placebo treatment is superior to that of another placebo, different outcomes are expected.
Expectations may act in association with other factors, such as desire of relief and reduction of anxiety. In other words, placebo phenomena occur within the context of emotional regulation, and symptoms should be influenced by desire, expectation, and intensity of emotional feeling (Price et al., 2008).
Desire and expectation interact and underlie common human emotions like sadness, anxiety, and relief (Price et al., 1985, 2001; Price and Barrell, 2000), thus in the context of analgesic studies it is quite plausible that patients and subjects have some degree of desire to avoid, terminate, or reduce evoked or ongoing pain.
Benedetti, Fabrizio. Placebo Effects (pp. 119-120). OUP Oxford.
Kaptchuk TJ, Stason WB, Davis RB et al. (2006). Sham device vs inert pill: randomised controlled trial of two placebo treatments. British Medical Journal, 332, 391-7.
Linde K, Witt CM, Streng A, Weidanhammer W, Wagenpfeil S et al. (2007). The impact of patient expecations on outcomes in four randomizes controlled trials of acupuncture in patients with chronic pain. Pain, 128, 264-71.
Price DD, Finniss DG and Benedetti F (2008). A comprehensive review of the placebo effect: recent advances and current thought. Annual Review of Psychology, 59, 565-90.
Price DD and Barrell JJ (2000). Mechanisms of Analgesia produced by hypnosis and placebo suggestions. Progress in Brain Research , 122, 255-71.
Price DD, Barrell JE and Barrell JJ (1985). A quantitavtive-experiential analysis of human emotions. Motivation and Emotion, 9, 19-38.
Price DD (2001). Assessing placebo effects without placebo groups: an untapped possibility? Pain, 90, 201-3.