CAM: what is evidence?

The only way to find out whether a health treatment works and is safe is to test it. The results of these tests are called evidence. Evidence can help you when you’re deciding whether to use a complementary and alternative medicine (CAM).

What do we mean when we say a health treatment 'works'?

In these articles, when it says treatment 'works' it means that in fair scientific tests the treatment has been shown to perform well. This typically means better than a placebo, or fake, treatment, or better than other treatments currently in use.

    Scientists often use the word 'efficacy' in the same way. In cases where the treatment performs better than placebo, they say it has been shown to be 'efficacious'.

      Scientists use the word 'effective' to describe a treatment that is being seen to produce a beneficial effect in the real world, outside of clinical trials. Health treatments can produce beneficial effects in the real world for many reasons, including the placebo effect.

      Every day, we make decisions by using our common sense and intuition. But when choosing between different health treatments, these tools are often not enough.

      For example, we may hear from a friend that a particular alternative treatment helped improve her asthma. At first, there might seem an obvious conclusion: the treatment works. But beware: the experience of a single individual does not prove that a treatment works.

      Our friend may have been experiencing the placebo effect. Or the improvement may have had another cause, or been simply due to the passing of time. It's also important to remember that any medicine or treatment may work differently for different people.

      So how can we really judge whether a treatment is safe, and likely to work?

      The answer lies with the results of fair tests, which is evidence. Without evidence, we risk choosing treatments that don’t work, or, even worse, that can do us serious harm.

      The role of evidence in medicine

      Evidence plays an important role in conventional medicine.

      Practitioners of conventional medicine strive to use treatments that are supported by clinical evidence showing they are safe and that they work. Still, the use of treatments in conventional medicine is not always based on scientific evidence.

      In these cases, the use of treatment is based on the clinical experience and training of the health professionals – GPs, nurses, doctors – involved.

      Evidence, CAM and the NHS

      The National Institute for Health and Care Excellence (NICE) uses evidence when it draws up guidance for the NHS on the use of treatments and the care of patients.

      Currently, NICE recommends the use of a complementary and alternative treatment in a limited number of instances, including:

      • Alexander Technique for Parkinson’s disease
      • ginger and acupressure for reducing morning sickness
      • acupuncture and manual therapy, including spinal manipulation, spinal mobilisation and massage for persistent low back pain

      Gathering and using evidence

      The best way to produce good evidence on a health treatment is to conduct a fair test. Here, the medicine or treatment being tested is compared to another treatment, or to a fake version of the treatment, called a placebo. To learn more about the placebo effect, read What is the placebo effect?.

      Tests are made as fair as possible by minimising bias and the role of chance. That means that the test results will reflect, as far as possible, the truth about the medicine or treatment, and will not be influenced by other factors, such as the way the test was carried out, or the attitudes of the people who take part.

      Scientists often call these fair tests "clinical trials". You can learn more in our Health A-Z pages on clinical trials.

      Before scientists conclude that a health treatment is safe and that it works, there must usually have been several independent tests of the treatment that have shown this.

      Sometimes, different fair tests can give results that disagree.

      Evidence for and against

      The results of fair tests can provide:

      • Results that show the medicine or treatment does work, and is safe. This is often call positive evidence, or evidence for the treatment.
      • Results that show the medicine does not work, or is unsafe. This is often called negative evidence, or evidence against the treatment.

      Scientists usually like to see the results of a number of fair tests before they begin to draw conclusions.

      It is important to remember that negative evidence – that is, evidence against a treatment – is not the same as no evidence. Negative evidence means a set of results showing that a medicine or treatment does not work. No evidence simply means an absence of any evidence, because fair tests have not been conducted.

      Where to find evidence

      You can read more about evidence by searching the NHS Evidence website.

      Page last reviewed: 06/02/2014

      Next review due: 06/02/2016


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      Next review due: 12/02/2016

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