I've seen many studies comparing proposed cures to placebo, but what about any studies actually investigating the effectiveness of placebo effect itself?
So, has there been any study as to the effectiveness of placebo in ameliorating certain affliction' symptoms, compared to no treatment at all? In which illnesses has it been determined to be most potent?
There are numerous studies where there was a control group with placebo and control group without placebo (on top of whatever was being tested against placebo, aka "active treatment" group). The data from such study can be easily cleansed of "actual drug" third group and turned into placebo vs. nothing efficacy comparison.
There are also studies which only use placebos, some telling the patient that it's placebo, some not telling them.
Here's one example of the comparison of the two approaches: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3008733/?tool=pmcentrez
Placebos without Deception: A Randomized Controlled Trial in Irritable Bowel Syndrome Ted J. Kaptchuk, etc...
Findings
Open-label placebo produced significantly higher mean (±SD) global improvement scores (IBS-GIS) at both 11-day midpoint (5.2±1.0 vs. 4.0±1.1, p<.001) and at 21-day endpoint (5.0±1.5 vs. 3.9±1.3, p = .002). Significant results were also observed at both time points for reduced symptom severity (IBS-SSS, p = .008 and p = .03) and adequate relief (IBS-AR, p = .02 and p = .03); and a trend favoring open-label placebo was observed for quality of life (IBS-QoL) at the 21-day endpoint (p = .08).
Conclusion
Placebos administered without deception may be an effective treatment for IBS. Further research is warranted in IBS, and perhaps other conditions, to elucidate whether physicians can benefit patients using placebos consistent with informed consent.
Here's another study showing placebo efficacy:
Levine JD, Gordon NC, Smith R, Fields HL (1981). "Analgesic responses to morphine and placebo in individuals with postoperative pain". Pain 10 (3): 379–89. doi:10.1016/0304-3959(81)90099-3. PMID 7279424
Abstract
The effects of placebo and varying doses of intravenous morphine were studied in 74 patients. All patients underwent extraction of impacted mandibular third molars. Two hours after onset of anesthesia all patients received a placebo (intravenous saline). One hour after the placebo administration each patient received either a second placebo or, 4, 6, 8 or 12 mg of morphine, double blind, via a hidden intravenous line. Pain level was evaluated 50 min after morphine administration using a visual analog scale. Pooled data from all patients produced a dose-response curve asymptotic by 8 mg. The mean pain relief following the second placebo was found to be between that obtained following hidden administration of 4 and 6 mg of morphine.
Hoffman GA, Harrington A, Fields HL (2005). "Pain and the placebo: what we have learned". Perspect Biol Med 48 (2): 248–65. doi:10.1353/pbm.2005.0054. PMID 15834197.
Not only do placebos often work better that no treatment - certain placebos are better than others!
Brand name pain relievers work better than generic ones, even though they have same active ingredients (Braithwaite and Cooper, 1981). Pills that patients consider more expensive are better than cheap ones, even when both are the same placebo (Waber et. al, 2008). The placebo effect is stronger when the same 'drug' was assumed to have worked before (Colloca and Benedetti, 2006) and when doctors expressed optimism in the outcome (Linde et al, 2007). Perhaps most amazingly, the colour of a pill actually influences the degree to which it works (Craen et. al, 1996)
