Placebo response

Placebo Effect Placebo Response Placenta Growth Factor... 

For some conditions, a large placebo effect can be anticipated. For example, studies of hormone replacement therapies for hot flashes in postmenopausal women consistently show a 50% decline from baseline in the number of daily hot flashes in the placebo group. Therefore, in order to show significance, an active treatment must produce an effect that is substantially larger than 50%. A marked placebo response is commonly observed with any condition that has a subjective component, such as chronic pain (e.g. arthritis), episodic pain (e.g. headaches), psychological states (e.g. anxiety), and certain physiologic measurements (e.g. blood pressure). 

Early landmark studies utilizing Hispanic subjects in the 1980s (Escobar Tuason, 1980 Marcos Cancro, 1982) compared the efficacy and response of several tricyclic antidepressants to placebo. They were the first to hint at a possible heightened placebo response in Hispanics and they suggested that certain Hispanic subjects... 

A pooled analysis of 14 875 adults (Hispanic, n = 361 White, n = 10 108 African American, n = 547 Asian, n = 112) who participated in 104 double-blind, placebo-controlled paroxetine trials for mood and anxiety disorders was performed to ascertain minority group differences (Roy-Byrne et al., 2005). There were significant differences in rates of response by ethnicity (p = 0.014) with the odds of responding being lower for the Asian and Hispanic subjects compared to the African American and White subjects. There was also a higher placebo response rate in Hispanic subjects. Rapidity of response and emergence of adverse effects were similar across groups. 

These continuation trials tell a very different story from that told by relapse-prevention trials. They show that there is little difference between antidepressant and placebo even when the clinical trial is extended over a longer period of time. Across the eight continuation trials that have been published, 79 per cent of patients on placebo and 93 per cent of patients on active medication remained well throughout the treatment period. In these long-term studies, placebo treatment was 95 per cent as effective as drug treatment. The authors of a meta-analysis of these trials concluded that the widely held - and probably erroneous - belief that the placebo response in depression is short-lived appears to be based largely on intuition and perhaps wishful thinking .17... 

Goetz, Christopher G., Joanne Wuu, Michael P. McDermott, Charles H. Adler, Stanley Fahn, Curt R. Freed, Robert A. Hauser, Warren C. Olanow, Ira Shoulson, P. K. Tandon, Parkinson Study Group and Sue Leurgans, Placebo Response in Parkinson s Disease Comparisons among 11 Trials Covering Medical and Surgical Interventions , Movement Disorders 5 (2008) 690-99... 

Khan, Arif, Nick Redding and Walter A. Brown, The Persistence of the Placebo Response in Antidepressant Clinical Trials , Journal of Psychiatric Research 42, no. 10 (2008) 791-96 Kihlstrom, John F., Attributions, Awareness and Dissociation In Memoriam Kenneth S. Bowers, 1937-199 6 , AmericanJournal of Clinical Hypnosis 40, no. 3 (1998) 194-205... 

Expectancy in the Placebo Response , Pain 43 (1990) 121-28 Waber, Rebecca L., Baba Shiv, Ziv Carmon and Dan Ariely, Commercial Features of Placebo and Therapeutic EfficacyJournal of the American Medical Association 299, no. 9 (2008) 1016-17 Wager, Tor D., The Neural Bases of Placebo Effects in Pain , Current Directions in Psychological Science 14, no. 4 (2005) 175-79... 

Hyaluronic acid injections temporarily and modestly increase synovial fluid viscosity and were reported to decrease pain, but many studies were short term and poorly controlled with high placebo response rates. 

In 1995, Prescrire International, a French journal that evaluates pharmaceutical products, published a review that concluded "As homeopathic treatments are generally used in conditions with variable outcome or showing spontaneous recovery (hence their placebo responsiveness), these treatments are widely considered to have an effect in some patients. However, despite the large number of comparative trials carried out to date there is no evidence that homeopathy is any more effective fhan placebo therapy given in identical conditions." ... 

A positive placebo response (particularly a large one) is well recognised in the condition to be treated. 

Previous studies have convincingly defined the placebo response rate, and the study is designed to test dose-response or activity against a positive control. 

Some disease states or trial conditions militate in favour of a high placebo response rate and lend support for the inclusion of placebo in a comparative trial. These include long treatment periods, previous treatments and response to them, innate characteristics of the study subjects (e.g. social class, educational level and personality t)rpe), influence of medical staff, environment and supervision during the trial, appearance and taste of trial drugs, and presence (or absence) of imwanted pharmacological effects. 

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