Is it Effective? Is it Safe? The Importance of Scientific Evidence

Someone looking for a new car might turn to test results in a consumer magazine to see how safe or reliable a certain car is. In the same way, health care providers turn to the scientific evidence to see how safe and effective a complementary therapy may be.

Because complementary therapy is such a broad field, the quality of the scientific evidence can vary from one therapy to another. For some therapies there is good evidence on safety and effectiveness. For many others there is limited evidence, making it hard to draw conclusions.

Weighing the scientific evidence

While there are many ways to assess the quality of the scientific evidence, most look at:

• The types of studies done
• The number of studies done
• The consistency of findings across studies

Together, these three basic factors form the weight of evidence behind a therapy and help answer important questions about its safety and effectiveness.

Types of studies

There are many types of research studies. Some hold more weight than others when it comes to the importance of their results. In general, randomized controlled trials are considered the best type of study for determining whether a treatment is safe and effective. Prospective cohort studies and case-control studies also can be used to assess complementary therapies. Learn more about different types of research studies.

In addition to study type, study quality and study size (the number of people taking part in a study) are also important. The results of a small, poorly-designed randomized controlled trial may be viewed as weaker than those of a larger, well-designed cohort or case-control study.

Number of studies

The greater the number of studies on a complementary therapy, the more evidence there is from which to draw conclusions about its risks and benefits. Of course, the type, quality and size of the studies are important too. One large, well-designed randomized controlled trial can be more compelling than 20 small studies. In general, though, the more studies there are on a therapy, the more health care providers and scientists are able to draw conclusions about its safety and effectiveness.

Consistency of findings

How consistent findings are across studies—whether or not they tend to show the same results—is important in weighing the evidence on a complementary therapy. Evidence is more compelling when most studies have similar results. When the results from half the studies show a therapy is effective and the results from the other half do not, it’s hard to draw conclusions. It's similar to asking three friends what they thought of a new movie. If all three liked it, you have evidence that the movie was good. If one friend liked it, one didn't and one thought it was OK, it's hard to know what to think.

Natural Standard’s grading system for complementary therapies

Susan G. Komen for the Cure® licenses the content on individual complementary therapies from Natural Standard. Within each discussion of all the therapies, an “A” through “F” grading system (see below) is included to assess the weight of evidence for its effectiveness. "A" indicates strong evidence that a therapy is effective. "C" indicates unclear or mixed results. "F" indicates strong evidence that a therapy is not effective. And, "B" and "D" indicate the evidence falls in between the other grades.  

Growing evidence

Complementary therapy is a dynamic field with new studies continuing to add to our knowledge. The weight of scientific evidence on many therapies is building quickly. As important studies are published, more refined conclusions can be drawn about the safety or effectiveness of these therapies.

See a list of complementary therapies discussed in this section.

Updated 01/27/11

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