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  • The Scientific Evidence Behind Complementary Therapies


    Someone buying a new car might look at test results on a consumer website to see whether a certain car is safe and reliable. In the same way, health care providers look at the scientific evidence to see how safe and effective a complementary therapy may be.  

    The quality of the scientific evidence varies from one complementary 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:

    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 strength of their results. In general, randomized controlled trials are considered the best type of study for learning whether a complementary therapy is safe and effective. Prospective cohort studies and case-control studies also can be used to assess complementary therapies.  

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

    Learn more about different types of research studies.  

    Learn more about study size.  

    Number of studies

    The more studies on a complementary therapy, the more evidence there is 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 better health care providers and researchers are able to draw conclusions about its safety and effectiveness.  

    Consistency of findings

    Whether or not studies 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 some studies show a therapy is effective and the results from other studies do not, it's hard to draw conclusions. It's similar to asking three friends what they thought of a movie. If all three liked it, you have evidence 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.

    Growing evidence

    New studies continue to add to our knowledge of complementary therapies. As more studies are published, we are better able to draw conclusions about the safety and effectiveness of these therapies.

    Limited data on safety

    All decisions about complementary therapy use should be made jointly with your health care provider. Few complementary therapies have been studied with the same scientific rigor as standard medicine. While some are safe, others should be avoided. For example, some therapies can [8-12]:

    •  Interfere with the effectiveness of chemotherapy and radiation therapy  

    •  Increase surgical risks 

    • Worsen treatment side effects

    Some therapies are safe at lower doses, but harmful in higher amounts. Talking with your provider before using any complementary therapy may help avoid problems and ensure all the risks and benefits to your health are carefully considered.  

    Learn more about talking with your provider about complementary therapies.  

    Learn more about the safety of complementary therapies.  

    Updated 06/24/14

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