Dr Dingle's Blog / nnt
Medical statistics are often used to justify the overuse of pharmaceuticals because they use different types and they are hard to understand then there is even a simpler number which is used in medicine, the Number Needed to Treat (NNT). This is how many people you need to treat to stop one negative outcome occurring. The negative outcome might be heart attack, stroke, cancer or even recurring ear infection. The NNT offers a measurement of the impact of a medicine or therapy by estimating the number of patients that need to be treated in order to have an impact on one person. In this case the higher the number the worse it is and the lower the number the more effective the medication. So an NNT of 1 is fantastic and an NNT of 100 is absolutely useless.
If a new drug reduced the death from heart attacks by say 50% (absolute statistics) then the number needed to treat is around 2 (NNT =2). So you only need to treat two people to have a benefit and save one life. This is great. If the new drug cuts the heart attack rate by only 25%, that is 1 in 4 then the NNT is 4. If the drug is only one percent effective which means of the 100 people given the drug it will only potentially (remember we are not even considering the side effects here) save one life, like the statin drugs, then the NNT is 100.
Fortunately the NNT is well established in medicine but not widely promoted. One website however TheNNT.com puts all this information in one place. Even for the most skeptical GP’s and specialists and it is available free to everyone. Just as important it is a group of physicians, medical doctors, that have collected the information. They only use the highest quality, evidence-based studies (frequently, but not always Cochrane Reviews), and they accept no outside funding or advertisements so they are independent of pharmaceutical companies.
In addition, for every therapy they review, they provide a color-coded summary for you to use (borrowed from the traditional stoplight). Unlike most sites this group also report harm that may be caused by the drug or the procedure and then they rate them into a stoplight colour coded. They have developed a framework and rating system to evaluate therapies based on their patient-important benefits and harms. The therapies rated green are the best you can get – there is clear evidence of benefits which clearly outweigh any associated harms. For example: Steroids for Asthma Attack: if you give steroids to 8 patients with asthma attack in the emergency department, you prevent one from having to be admitted to the hospital. There are definitely side effects to steroids – high blood sugar, hyperactivity – but are considered minor in comparison. The NNT for this treatment is 8. Remember the lower the number the better. Therapies rated yellow require more study because they don't think the data is conclusive or substantial enough to be able to give a clear rating yet. So they are not recommended but if you do use them go with caution. Red suggests that while there may be some benefits, they are far outweighed by the harms. One extreme example: if a medicine were to save 2% of people's lives, but cause strokes in 10% of people, it's hard to say that this medicine clearly is overall helpful. Black is the "worst" or "lowest" rating. Therapies rated black have very clear associated harms to patients without any recognizable benefit. What is frightening is that most of the major medications and procedure used for cardio vascular disease fit into the black.
While there are many drugs and procedures listed I will start with some of the common procedure for cardio vascular disease as this is the biggest killer and there is just not enough space here to cover all the listings on TheNNT.com web site. For statin drugs for acute coronary syndrome the NNT is 0% in other words no person who took the drug were helped (life saved; heart attack, stroke, or heart failure prevented) however, an unknown number were harmed (medication side effects/adverse reactions). This was put on the black list. Statins Given for 5 Years for Heart Disease Prevention (With Known Heart Disease) NNT was 83. In fact they reported 96% saw no benefit however 1% were harmed by developing diabetes and 10% were harmed by muscle damage, just two of the side effects. This is also put on the black list as the harm outweighs any insignificant benefit of the drugs. Statin Drugs Given for 5 Years for Heart Disease Prevention (Without Known Heart Disease) also put on the black list and has a NNT of 104 for non-fatal heart attack but they reported 0% life saved and 1 in 100 were harmed, they develop diabetes and 1 in 10 had severe muscle damage. In contrast, they reported the Mediterranean Diet for Secondary Prevention After Heart Attack got the green light and a NNT of 30 for mortality and no negative side effects and as low as 1 in 18 were helped. Not to mention the other benefits in other conditions such as cancer and diabetes.
Beta Blockers for Acute Heart Attack (Myocardial Infarction) are also commonly prescribed by specialists are put on the black list and listed with no benefit, but 1 in 91 were harmed by cardiogenic shock. Hormone Replacement Therapy for Cardiovascular Prevention of a First Heart Attack or Stroke, black list and no benefit found but 1 in 250 were harmed (heart attack due to HRT oops, exactly what they were supposed to prevent), 1 in 200 were harmed (stroke due to HRT) and 1 in 100 were harmed (blood clot in the leg/lung). To support this a recent study which investigated 27 trials found only one trial showing a 0.7% benefit and 26 trials that suggest no aggregate mortality benefit to beta-blockers. All the more recent, and larger, trial that utilized double-blind techniques (COMMIT, 2004) found no benefit.
Even putting a stent (a little piece of artificial artery) in an artery got on the black list. In the case of Coronary Stenting for Non-Acute Coronary Disease Compared to Medical Therapy none were helped, that is no life saved, no heart attack prevented, and no symptoms reduced, however, 1 in 50 were harmed including complications such as bleeding, stroke, kidney damage. Coronary Artery Bypass Graft Surgery (Heart Bypass) for Preventing Death over Ten Years was marginally better. The NNT was 25 to prevent death however, 1 in 83 died, 1 in 100 had stroke, 1 in 43 had kidney failure, 1 in 28 in the operation, 1 in 14 required extended life support and get this, 1 in 3-5 had cognitive decline. Not such a good outcome if you look at the whole picture and any wonder it was put on the black list
Aspirin Given Immediately for a Major Heart Attack (STEMI). Got the green light. So if you have a heart attack taking an aspirin straight away has some benefit. The NNT was 42 for mortality as 1 in 42 were helped (life saved) but 1 in 167 were harmed (non-dangerous bleeding). However, with Aspirin to Prevent a First Heart Attack or Stroke the NNT was 1667 for cardiac benefit, that is 1 in 1667 were helped (cardiovascular problem prevented), 1 in 2000 were helped (prevented non-fatal heart attack) and 1 in 3000 were helped (prevented non-fatal stroke). But no deaths prevented and 1 in 3333 had a major bleeding event.
The NNT for Blood Pressure Medicines for Five Years to Prevent Death, Heart Attacks, and Strokes were 125, 1 in 67 prevented stroke, and 1 in 100 prevented heart attack. However, 1 in 10 had side effects and stopped taking the drug. Treatment of Mild Hypertension for the Primary Prevention of Cardiovascular Events was given the yellow light and the there was no NNT as no benefit was found. However, 1 in 12 experienced medication side effects.
On a positive note oral anticoagulants (warfarin) for primary stroke prevention (no prior stroke) got the green light and the NNT was 25 for prevented stroke and 1 in 42 were helped (preventing death from any cause). However, 1 in 25 were harmed (having bleeding), 1 in 384 were harmed (intracranial hemorrhage).
It seems we spend billions of dollars, even trillions of dollars on drugs and procedures that don’t work and and are likely to be doing more harm than anything just because of trust and a lack of knowledge on statistics. While I am likely to criticized for presenting this information and you might question your doctor or specialist, remember I am just the messenger presenting factual numbers. See for yourself www.TheNNT.com.