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NCCIH Clinical Digest

for health professionals

Know the Science of Complementary Health Approaches: What the Science Says

October 2023

Clinical Guidelines, Scientific Literature, Info for Patients: 
Know the Science of Complementary Health Approaches

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The National Center for Complementary and Integrative Health’s (NCCIH’s) “Know the Science” initiative is a resource to help consumers better understand complex scientific topics related to health research. It can help them be discerning about what they hear and read so they can make well-informed decisions, especially about complementary and integrative health, where many approaches are readily available in the marketplace and are often selected for self-care. The Know the Science initiative covers topics such as how to make sense of a scientific journal article, medication-supplement interactions, facts about health news stories, the placebo effect, health-related risks, and the myths about “natural” products.

Here are 10 “Know the Science” facts to help your patients get to know the science of health:


Did You Know?

  1. Some online sources of information on complementary health approaches are useful, but others are inaccurate or misleading. If you're visiting an online health site for the first time or downloading a new app, ask these questions: Who runs or created the site or app? Can you trust them? What is the site or app promising or offering? Do its claims seem too good to be true? When was its information written or reviewed? Is it up-to-date? Where does the information come from? Is it based on scientific research? Why does the site or app exist? Is it selling something?
  2. Unless you read and understand the original sources for a health news story, it can be difficult to know whether a news story is misleading or has left out important information. But the likelihood that the story is correct increases if it comes from a media outlet that isn’t trying to promote a point of view or cause, was written by a science or health reporter trained to understand medical findings, and includes quotes from experts not connected to the study (for a more objective take on the findings or to show another point of view).
  3. Sometimes taking a prescription medication and dietary supplement together may increase the drug’s effects. Sometimes, taking a medication and a supplement together may increase a medication’s effects. This can result in the medication being too strong and raise the risk of unwanted side effects. For example, glucosamine may increase the effects of anticoagulants (blood thinners) such as warfarin (Coumadin), which can increase the risk of serious bruising and bleeding. Ashwagandha seems to have sedative effects, and there is some preliminary evidence that it may increase the effects of some benzodiazepines (e.g., Valium, Xanax) and other sedatives and anti-anxiety drugs.
  4. Sometimes taking a prescription medication and a supplement together may decrease the drug’s effects. This means that you aren’t getting the full benefit from the medication that your health care provider wants you to have. The popular herbal supplement St. John’s wort is known to decrease the effects of drugs. It does this by speeding up the processes in your body that change drugs into inactive substances. Recent research found that levels of metformin (the most commonly prescribed medication for people with type 2 diabetes) decreased about 25 percent in healthy adults who were given goldenseal extract plus metformin. This drop was enough to potentially hinder glucose control in people with type 2 diabetes taking metformin. In addition, green tea at high doses has been shown to reduce blood levels and therefore the effectiveness of the drug nadolol, a beta-blocker used for high blood pressure and heart problems. It may also interact with other medicines.
  5. When it comes to medicine, there is no official definition for use of the term natural. And it’s important to know that a medicinal product labeled natural does not always mean safe. For example, the herbs comfrey and kava may be considered natural products, but they can cause serious harm to the liver. 
  6. Although many herbal or dietary supplements (and some prescription medications) come from natural sources, “natural” does not always mean that it’s a better option for your health. An herbal supplement may contain dozens of chemical compounds, and all of its ingredients may not be known. Scientists are studying many of these products to identify what ingredients may be active and to better understand their effects in the body.
  7. Clinical trials to test whether a treatment is useful and safe in humans may vary in size and type. While all research studies are important and contribute to our knowledgebase, clinical trials are the types of studies you probably hear about most often in the news. They can have the most immediate impact on improving health and treating disease. Well-planned clinical trials are done with people and may vary in size and type. Clinical trials give the clearest information about whether a treatment or a lifestyle change is effective and safe in humans. However, because they are complicated, lengthy, involve many research participants, and can be very expensive, they are usually done only after smaller preliminary studies have been completed.
  8. The number of people participating in a study, or the sample size, can affect the outcome of a study and what the results mean. Small sample sizes may produce inconclusive results and are more likely to produce results due to chance. Large sample sizes may give more reliable results and may better reflect the population. Large sample sizes may increase the chances that the result was accurate.
  9. The strongest evidence about whether a treatment is useful and safe consists of results from several studies by different investigators. A single study rarely provides a final, definitive answer. Repeating a study using the same methods with different volunteers and investigators helps us know that the results are reliable and valid.
  10. When looking for information from a study published in a medical journal, look at the date of the study. Was it conducted in the past year? 5 years? 15 years? As new information is learned, scientific standards and techniques change, and practices evolve. New research may support results from older studies as well as lead to new methods to diagnose and treat conditions and diseases. New research can, at times, also contradict other research, which may require additional research to explore and resolve these differences. Research can separate the good results from the bad results. In this way, the scientific method is self-correcting, which is reassuring. Looking at the date can provide insight into how the study fits into the larger evidence base on a particular topic.

NCCIH Clinical Digest is a service of the National Center for Complementary and Integrative Health, NIH, DHHS. NCCIH Clinical Digest, a monthly e-newsletter, offers evidence-based information on complementary health approaches, including scientific literature searches, summaries of NCCIH-funded research, fact sheets for patients, and more.

The National Center for Complementary and Integrative Health is dedicated to exploring complementary health products and practices in the context of rigorous science, training complementary health researchers, and disseminating authoritative information to the public and professionals. For additional information, call NCCIH’s Clearinghouse toll-free at 1-888-644-6226, or visit the NCCIH website at NCCIH is 1 of 27 institutes and centers at the National Institutes of Health, the Federal focal point for medical research in the United States.


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