Earlier I have shown why the placebo effect does not exist in a strict sense and that it is rather a mind effect and how we can make best use of the powers of mind. Now it is high time to ask what we can expect of these powers.
Some guess that roughly one third of a medical treatment success is due to the placebo effect. They rely on a publication by Henry K. Beecher, «The Powerful Placebo», back in 1955. Beecher had analyzed the outcomes of fifteen medical trials, concluding that 35 percent of the patients had improved by placebo alone. Forty years later, two German scientists have re-analyzed Beecher's data and found that he had misinterpreted them, saying that «no evidence was found of any placebo effect in any of the studies cited by him».
Placebo work best in pain and subjective outcomes
In 2001, two Danish scientists have analyzed 130 medical trials with a total of more than eight thousand patients. In trials where the outcomes have been yes (improved) or no (not improved), no placebo effect has been detectable. But in trials where the outcomes have been a degree of how much the patients improved, an effect of placebo has been detected in roughly a third of the cases, compared to no treatment. But this has been the case only in subjective outcomes, as rated by the patients, and in trials with pain. In 2004, the authors have updated their review with 42 new trials, extending the data pool to more than eleven thousand patients. For trials with patient-reported outcomes, a placebo effect has been detected in 30 percent of the cases, but only in 10 percent of the cases where the outcome has been reported by a doctor. Conclusion: The placebo effect works best in subjective conditions like pain or mental well-being.
Placebo effect of psychoactive drugs
In antidepressants, a very large amount of benefit may be due to the placebo effect. In a total of more than nineteen thousand patients where antidepressant drugs have been tested against placebo, it came out that the antidepressants have reduced the depressive symptoms by 40 percent and the placebo have reduced them by 30 percent.
Placebo effect against heart attack
In a study with more than a thousand men where a drug to prevent heart attack has been tested against placebo, not all patients have taken the pill as prescribed. Of the good adherers to the therapy, 15 percent died within five years, compared to 25 percent of the bad adherers. Interestingly, this has also been the case in the placebo group: 15 percent of the good placebo adherers have died versus 28 percent of bad placebo adherers. Similar results have been obtained in a study with more than sex hundred women.
Colin Sutton from Australia has sent me a mail, stating that "it's nothing to do with what they were taking. (...) the compliant patients were more likely to be following other healthy regimes - regular exercise, diet or whatever, than those that don't adhere to a plan". I agree that this may be one explanation, but possibly not the only one. (September 5, 2007)Take home message: The placebo effect can be powerful on a subjective level, mainly against pain and mental conditions.
Placebo effect: How to make best use of it
Placebo effect: There is no such thing
Photo credit: Wellcome Library, London