Inaccurate contraceptive info from National Prescribing Service

One of the key pieces of information we need when choosing contraception is accurate data on effectiveness. What is the likelihood that your birth control will stop you getting pregnant? We are presented with pretty charts by family planning counsellors, doctors, midwives; sometimes we are told a little more about “real world” and “perfect use” efficacy; if we’re lucky, our healthcare workers will do a more individual assessment, giving clear information on how medications, herbal medicines, weight, and other factors might affect contraceptive efficacy.

But how much do we really know about contraceptive failure rates? What do our doctors and nurse practitioners and midwives know? What sources of information are they drawing on? How accurate are those sources? I’ve typically thought that the sources offered in medical schools and textbooks and review journals and Family Planning leaflets were pretty good; the fact that they took into account real-world differences in use and misuse lent further credibility. Recent information has disabused me of that notion.

The National Prescribing Service (NPS) is a government-funded service in Australia intended to provide practitioners and consumers with independent, evidence-based, accurate education on the Quality Use of Medicines (QUM). It is a service with a lot of reach, and is considered by many doctors to be a rigorous and highly trusted source of medical education. They put out regular bulletins to doctors with information on both new and old drugs.

They have some “information” on contraception that didn’t ring true to me. The chart is large, so I’ve picked out the relevant parts – you can click through for a PDF of the full chart.

See that? Combined oral contraception (COCP, or what most people call the standard “Pill”) is cited has having a typical-use failure rate of 8% in the first year; a perfect-use failure rate of 0.3%. Progesterone-only oral contraception (POP, the “mini pill”) is cited as having a typical-use failure rate of 8 in the first year and a perfect-use failure rate of 0.3. The vaginal ring with combined hormones is cited as having a typical-use failure rate of 8 in the first year and a perfect-use failure rate of 0.3.

Do you smell a rat too?

[Click through for details on actual rat, size of rat, smelliness of rat, and where the rat came from!]

So I chased and I googled and I tracked, and I think they’ve just grabbed some contraceptive efficacy data from the World Health Organisation (WHO) website and slapped it in.

See if you can spot the problem with this.

I’ve excerpted just the barrier and certain female hormonal methods to highlight the problem.





Table 1. Percentage of women experiencing an unintended pregnancy during the first year of use and the percentage continuing use at the end of the first year, United States of America.
Method % of women experiencing an unintended pregnancy within the first year of use % of women continuing use at one year
  Typical use Perfect use  
Cap, Parous women 32 26 46
Cap, Nulliparous women 16 9 57
Sponge, Parous women 32 20 46
Sponge, Nulliparous women 16 9 57
Diaphragm 16 6 57
Female Condom (Reality) 21 5 49
Male Condom 15 2 53
Combined pill and minipill 8 0.3 68
Combined hormonal patch (Evra) 8 0.3 68
Combined hormonal ring (NuvaRing) 8 0.3 68
Source: Trussell J. Contraceptive efficacy. In Hatcher RA, Trussell J, Stewart F, Nelson A, Cates W, Guest F, Kowal D. Contraceptive Technology: Eighteenth Revised Edition. New York NY: Ardent Media, 2004.

The chart gives identical – not just similar, but identical – figures for failure and discontinuation rates of the combined pill and minipill, the contraceptive patch, and the contraceptive ring, both in typical use and perfect use situations. Typical use failure rate of 8%, perfect use failure rate of 0.3%, discontinuation rate of 68%.

This has get to set any half-tuned bullshit-meter a-ringing. There is no study that separates those types of hormonal contraception out, looks at them independently, and comes up with identical rates across the board. They have taken aggregated data for hormonal contraception, then split it for this table.

(The data for nulliparous women using sponges and caps is also identical, and the diaphragm data is close. This also smells.)

The table in the National Prescribing Service educational material for doctors is even worse – they’ve grabbed the data from this WHO table or its source, then further split out the combined oral contraceptive pill and minipill, attributing them identical failure rates also. Doctors are reading this and “learning” that the minipill (progesterone only pill) is exactly as effective as the combined oral contraceptive pill, then making prescribing decisions on that basis.

You can’t grab aggregate data and assume that it applies equally to every subset. That would be like saying that each and every adult human has slightly less than one breast.

I source-chased a little further. With help (thankyou!) I have a Trussell review paper with this chart in it. I have cut it to the relevant parts; click through to see the full chart.

James Trussell, “Contraceptive failure in the United States”, Contraception, 2004, 70(2):89-96.

Here are the notes from that source.

“For spermicides, withdrawal, periodic abstinence, the diaphragm, the male condom, the pill and Depo-Provera, these estimates were derived from the experience of women in the 1995 NSFG, corrected for underreporting of abortion, so that the information pertains to nationally representative samples of users [3]. …

“The NSFG does not ask for brand of pill; thus, combined and progestin-only pills cannot be distinguished. However, because use of the combined pill is far more common than use of the progestin-only pill, the results from the NSFG overwhelmingly reflect typical use of combined pills. The efficacy of progestin-only pills may be lower than that for combined pills because progestin-only pills are probably less forgiving of nonadherence to the dosing schedule. […]

“The estimates for the Ortho-Evra patch and NuvaRing were set equal to those for the pill. It is possible that the patch and ring will prove to have better efficacy than the pill during typical use, because of better adherence with the dosing schedule. However, such superior efficacy has not been demonstrated in randomized trials. […] There are no published studies in which women were randomly assigned to the NuvaRing and the pill. Clinical trials of Lunelle cannot yield an estimate of efficacy during typical use, because the design of those trials calls for discontinuing those who return late for their injections [7,8]; the estimate is therefore assumed to be the same as that for Depo-Provera.”

Suspicion confirmed. The NPS comparison-chart information on contraceptive efficacy is not evidence-based; it’s based on a series of assumptions and estimates and aggregations, and an error of baseless disaggregation that I can’t call anything but egregious.

Your health dollars at work. Your body at risk.


If you’re not an Australian local, where are you getting your information on contraceptive efficacy? What does it say? Where does it come from – both immediately, and originally?

Categories: gender & feminism, medicine, Science, skepticism

Tags: , , , , , , , , , ,

9 replies

  1. Excellent. As if there aren’t sufficient problems with dodgy doctors, even those who genuinely try to stay on top of the situation can be misled by someone not doing their job properly.

  2. ROUSes galore, right here in the medical profession. And you thought they didn’t exist. ;-P Where’s a fireswamp when you need one?

  3. That’s worrying.
    The info I have, from a leaflet by the Family Planning Association (UK), is quite vague – all hormonal methods of contraception are put as 99% effective, with no ‘typical use’ rates given.
    The two key concerns for me are the rates of effectiveness for treating PMS, and for increased risk of breast cancer, which it doesn’t really address.

  4. They also should be educating doctors that women who weigh over 70kg should be taking TWO Microlut/mini-pill tablets daily to ensure efficacy. The doctors at the local Family Planning clinic knew this and showed me the new recommendation in the guidelines Australian doctors are given regarding contraception, but my GP hadn’t heard this and neither had any of the other doctors at their practice.
    It’s a little piece of fat bias in action too. If you need a larger than usual dose of most medication, the doctor can call Medicare and get an authority number to prescribe you the extra dose for the same cost as the regular dose. There is no authority number for the required double dose of Microlut.

  5. And yet – despite the average bodyweight of an Australian woman being around 68-70 kg – there is not yet any “Minipill Plus” type formulation with a double dose. Nearly half the POP-using population is left either paying double for their contraception, or worse being not informed of the need for an appropriate dose.

  6. That would have been useful to know when I was well over 70kg and trying not to get pregnant. No one ever said that though, they just told me to lose weight. At least the problem will be ‘snipped’ in the bud soon.

  7. Wow, lucky I’m playing it paranoid and Dutch, then. Though I *really* don’t want to raise this with a doctor :-/

  8. I’d be interested to hear if I got the same information/advice about the mini-pill, since at my height 70kg would be a very low bodyweight, probably around about the point where I’d stop menstruating. It may be a contraceptive option I consider after pregnancy, I will raise it with my doctors and find out what their awareness is. (Tall people don’t get any equivalent of fatphobia, in fact we’re privileged in various ways because it’s a male-associated trait, but I do have repeated problems with medical practitioners having difficulty with prescriptions and test results because there is not enough data for women of my height/weight/blood volume. The way this is discussed for me versus someone shorter but with the same weight would be instructive.)
    In general, I (in Australia) have found that GPs have been very uninterested in discussing contraceptive choice with me, except for one who was horrified to hear that I was using barrier methods only at some point. The discussion has never got near the level of percentage failure rates, let alone the perfect/typical use distinction. I’ve never been offered literature of any kind on contraceptive choice. I used Nuvaring for a year or so but had to be referred to a gynaecologist for the prescription, because the GP was convinced and remained convinced after several explanations that it was a new type of IUD. (Yeah, good time for a new GP, but both I and my GPs move suburbs often enough that it seems that I do a big search only to immediately have to do another one.)

  9. For those following this conversation – we’re also discussing it at the crosspost on Shakesville. I’ve unearthed some Canadian stuff that may be the source of the error (or maybe they copied from us).

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