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Thank you for your patience as we update NAT content for you. Our new format will help you quickly find evidence-based information about supplements and natural therapies.

Our first step continues to be a search for quality research. The research is carefully reviewed and objectively assessed. The information is then synthesized to see whether a supplement or therapy is:

  • Likely Effective—good evidence points to a benefit.
  • May Be Effective—evidence shows a trend toward a benefit. More evidence is needed.
  • May Not Effective—evidence shows trend toward a lack of benefit. More evidence is needed.
  • Unlikely to Be Effective—good evidence has shown the treatment is not effective.

The level of evidence for each category is as follows:

Likely Effective
  • ≥ 3 moderate to large (≥ 60), well-designed* Randomized Control Trials (RCT) supporting effectiveness, OR
  • ≥ 1 meta-analyses of ≥ 3 such trials supporting effectiveness, AND
  • Absence of contradictory trials or meta-analyses
May Be Effective or May Not Effective
  • 1 or 2 moderate to large (≥ 60), well-designed RCT’s, OR
  • ≥ 2 small (< 60) otherwise well-designed RCT’s, AND
  • No meta-analyses of such trials, OR
  • Presence of contradictory trials or meta-analyses
Unlikely to be Effective
  • ≥ 2 moderate to large (≥ 60), well-designed RCT’s supporting ineffectiveness, OR
  • ≥ 1 meta-analyses of ≥ 3 such trials supporting ineffectiveness, AND
  • Absence of contradictory trials or meta-analyses
No Mention
  • No moderate to large (≥ 60), well-designed RCT’s OR
  • No meta-analyses of such trials, OR
  • < 2 small (< 60) otherwise well-designed RCT’s of any number, OR
  • Only non-RCT’s or poorly-designed RCT’s

* Well-designed RCT = low risk of 3 of the following 5 biases: allocation, performance, detection, attrition and reporting

Commonly asked questions:

Q: Why don’t you include treatments/supplements that only have 1-2 studies?

A: If we made a conclusion based on that 1 trial, we would have a false impression. Chance can play a role in study outcomes. If you do the same type of study 10 times, at least 1 may end with a different outcome. This is due to the way factors happened to come together for that one trials. For this reason, it is common to wait until there is more than 1 trial before a conclusion can be made. The more trials there are, the more reliable the conclusion is.

Q. What is a randomized control trial (RCT)? Why is it included?

A: An RCT is considered one of the most reliable types of studies. It controls factors that can play a role in how effective a treatment is. It also often compares the treatment against a placebo or other treatment. This gives us a better picture of benefits. Unlike other types of studies, an RCT can show a cause and effect link. The more people in the trial, the more reliable the results.

Q: What are meta-analyses and systematic reviews?

A: These reviews will collect information from a number of studies. The results are mathematically combined to paint a clearer picture of the treatment being studied. This provides a more reliable result than single studies. It can also help if there are conflicting studies. A review can make results clearer.

Q: Why aren’t all studies included?

A: Not all studies can show a direct cause and effect relationship. For example, observational studies will look for certain factors in a chosen group. But they do not control any other factors that can change an outcome. These studies can show a potential link but not cause and effect. Other studies may not be done in a recognized format or published in a peer journal. This means we do not know the quality of study and whether certain rules were followed. Finally, some studies focus on animals or tissue in a lab. Again, they may show an interesting connection but this does not mean it will work well in the human body. For example, a substance may kill germs in a lab but will it survive the human digestion system? Will there be harmful side effects in the body? Will it require massive doses to be effective? For these reasons, we do not include these types of studies in treatment assessment. However, we may briefly talk about this information in the general summary of treatments or supplements.

Q: I use a therapy/supplement that has helped me. Why don’t you have the benefit listed or say that it is not effective?

A: We are happy that you found a treatment that is working for you. NAT will only report research-based findings. Unfortunately, there are many natural and alternative treatments that have not been researched or do not have quality studies. We are happy to review any research you think has been overlooked and will continue to review literature for new studies. It is important that your medical team know about any supplements you take, since some may interfere with other treatment.

Revision Information

  • Reviewer: EBSCO NAT Editorial Team
  • Review Date: 01/2019