Number Needed to Treat – Does Your Drug Work?

Number Needed to Treat, or NNT is the number of people that have to take a drug in order for a single person to have a benefit.NNT

The concept of Number Needed to Treat or NNT may surprise you. If 500 people have to take a drug in order that 1 is spared a heart attack, isn’t that the same as saying: The drug is useless for 499 of 500 people that take it. Useless. Well, that’s only if the drug does no harm, but few drugs are this benevolent.

We expect things to work, especially when it comes to medicine. If you have a bacterial infection, an antibiotic will almost always get rid of it. So an antibiotic has an NNT of one. Vaccinations work pretty well, somewhere between an NNT of one and 10. A drug that did no good at all, would have a Number Needed to Treat of infinity.

At some point, the drug industry got the idea of selling drugs that only occasionally worked. This had great advantages for them. If the drug didn’t work—that’s your problem. They never said it would.

Actually they say things like: reduces heart attack 30%. That sells more pills. Saying it would only work 0.2% of the time wouldn’t sell much of anything.

The corollary to Number Needed to Treat is Number Needed to Harm, or NNH. Ask you friendly neighborhood drug company CEO what the NNH of his or her latest and greatest medical breakthrough is. Expect a blank stare. If there are side effects, they are always said rapidly and said to be ‘well tolerated’. There is an odd recent exception to this rule: TV adds for medications list so many side effects so prominently that the spiel is almost a punchline to its own joke to such an extent that the warnings are ignored by the consumer. Clever advertising men.

There are several competing Poster Boys for drugs that don’t work. We hate to pick on statins again. Actually that’s a bald faced lie, we love picking on statins and for good reason. Overall, they decrease all cause mortality for practically no one. Yet insurance companies will bawl out a doctor that doesn’t prescribe them.

NNT for statins. From the site theNNT.com, you can find NNT’s , and NNH’s for many drugs. For statins used on people with no existing heart problems, we have:

NNT to prevent a heart attack 104, NNT to prevent a stroke, 154. OK so far so good. A heart attack was prevented for 1 in a hundred, and a stroke in 1 in 150 or so, but was there harm?

NNH was 1 in 50 for diabetes, 1 in 10 for muscle damage (permanent muscle loss).

How did the pharmaceutical industry ever make something nice out of that? They have very good marketers. Probably in those 100 people, 3 were going to get a heart attack. However, if on statins, 2 did. Statins Provide 33% Reduction in Heart Attacks, scream the headlines. However, in the group of 100, two got diabetes, and 10 permanently lost muscle. But, what about loss of life? Well that’s  a wash. Statins don’t reduce all cause mortality. So if they decreased cardio death, they increased some other sort of death, could be diabetes, or cancer. At least with cardiovascular death there was a chance you would just ‘wake up dead’ which to anyone familiar with death counts as a ‘good death.’

If you want to consider death as an end-point—which it certainly is—the Number Needed to Treat to save one life is infinite for statins. They don’t save any. There is another element to the NNT story; you may not even be in the cohort for whom there is ever any benefit. Thus even if you like the 104-to-1 odds of benefit proper screening will tell you if you are that guy for whom there is even that chance for benefit and this gets hidden in the rush to treat everybody with statins.

Check out the TheNNT.com site. Don’t be put off by its medical looking nature. It’s interesting and informative, if not a bit disturbing.

Some others:

  • Here are NNT and NNH for beta-blockers, another standard drug millions are taking: NNT – infinity. No one is helped. NNH was 91: 1 in 91 experienced cardiac shock which often leads to death.
  • For vitamins, none were helped, none were harmed. We now know from larger, later studies even this is not true. Vitamin/supplement takers have a higher risk of cancer.
  • For aspirin as a heart attack stroke prevention remedy, the NNT was 2000 for a heart attack, 3000 for a stroke. Not a lot of protection. The NNH was 3000 for a major bleeding event. Basically this is a wash.
  • Mediterranean Diet: NNT was 61 for preventing heart attacks. NNH, none. Plus, in general, the Mediterranean diet is delicious.

If you doctor doesn’t know the NNT for a drug he is prescribing, he hasn’t done his due diligence. Help him; he needs it.

  2 comments for “Number Needed to Treat – Does Your Drug Work?

  1. Jim
    April 26, 2015 at 4:51 am

    More great info to help educate. I remember watching Dr. David Newman do a TED talk on “Truths That Last” regarding this subject. I believe he is affiliated with the NNT site. Everone should watch it – entertaining.

  2. Webb
    November 15, 2016 at 5:08 am

    As a heart patient I tried to tell my doctors , i couldn’t tale the beta blockers , I felt like I was dying. I have not arrthymic, and low blood pressure most of the times me, I do have LBBB with a pacer do to CHF from The LBBB. I feel as if the pacer has help me with the Block, again dr, tried to get to to take beta blocker refused again. I have also read heart patients with Block should not take the beta blockers
    .

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