Number Needed To Treat

TheKettleBellPhysioBlog, Evidence, Pain, Uncategorized0 Comments

When we take a medication we tend to think that its active ingredient is going to have a specific effect…but that’s frequently not the case, even though the medication may appear to work as expected.

Consumers aren’t told about the ‘Number Needed to Treat’ (NNT) which is the number of people who must take the medication as prescribed for the active ingredient to have the intended effect in one person.

What the NNT doesn’t tell us is how *much* benefit the medication may provide *if* you happen to be the one single responder in a group e.g. 5% reduction in pain, 10%, 30% 50% or more, and several other factors.

The NNT for plain old paracetamol to achieve a 50% reduction in post-surgical pain is about 5. That means that 5 people have to take paracetamol for one of them to have a 50% reduction in their pain. It won’t have any effect for the other 4 people in the group who also took it.

When I have a headache I always take 1000mg of paracetamol and it works EVERY time, and I usually have a 100% reduction in pain. Funny that.

Am I really always one of the 20% of responders?
How is it consistently 100% effective instead of just 50%?

My only concern is a headache. I don’t care about active ingredients, NNTs or effect sizes; the only thing I care about when I have a headache is getting rid of it. I know that it’s extremely unlikely that I’m getting 100% pain relief from the active ingredient – it’s not possible because the medication doesn’t do that. But…it works for me and I don’t like headaches so I’m not going to stop taking it.

If manual therapy provides effective pain relief and enables someone to feel more comfortable doing what they need to be able to do than they otherwise would have been, they don’t care how it works either.

Manual therapy can and does have profound effects on pain and function, but not through any ‘specific’ effect. A joint can be pushed or cracked at a specific level, in a specific direction, with a specific force, without having a ‘specific’ effect on anything. It can have profound non-specific neurophysiological effects (together with a huge range of other variables beside the technique itself which may all enhance the outcome) but the same result could be achieved by a range of other interventions.

In manual therapy, the challenge comes when someone *believes* that the intervention has a specific effect and becomes reliant or dependent upon it (or the person applying it).

I’m perfectly happy knowing that when I take Paracetamol it’s not doing what it claims on the box, because it works for me, it’s convenient, quick and cost-effective.

If manual therapy works for someone, how it works is irrelevant so long as they’re under no illusions about specific effects.

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