Do you remember the last time a doctor gave you a prescription? You most likely assumed the medicine would work effectively. It turns out, that’s not always the case.
This week, Wired magazine ran a fascinating feature article on a metric that can help doctors to decide whether a treatment is worthwhile. The metric is called number needed to treat, or NNT and it describes how many people would need to undergo a treatment for one person to benefit. (There is a similar number called number needed to harm, or NNH, which describes the likelihood of a medicine having an adverse effect. Used together, these two metrics can simplify the medical decision-making process.)
The Wired article offers several interesting – and sometimes surprising – examples of commonly prescribed medications, and their NNTs. For example, the NNT for using baby aspirin to prevent heart attacks in healthy adults is 2,000. That means for every 2,000 healthy adults who take a baby aspirin daily, one heart attack will be prevented.
Another example is the use of of IV proton pump inhibitors – drugs which block the production of acid in the stomach – to control bleeding in the gastric system. In this case, there is no evidence of anyone benefiting from this treatment.
There are also examples of treatments that are incredibly effective. Using rapid defibrillation for someone who is having a heart attack has a NNT of 2.5. In other words, for every 2.5 people who receive the treatment, on person is saved. And the NNT of using the drug zofran to stop someone from vomiting is 5.
Do you want to know more? A group of doctors has launched a web site that provides NNTs for a broad range of treatments. TheNNT.com uses systematic reviews – many from the Cochrane Collaboration – to assign NNTs to medical therapies with a simple green, yellow and red rating system to indicate which treatments are likely to be worthwhile.
The concept of NNT is certainly worth perusing, especially if you are currently receiving treatment for a medical condition. From the patient’s perspective, it is a great tool for developing realistic expectations of whether a treatment will be successful.
The next time you visit the doctor, ask about the NNT for any medicines that you are prescribed. While a metric should never dictate treatment decisions, it’s a great lens through which to view your health care choices.
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