@noahwg linked an article (or a blog post? It seems more like a blog post) in the NY Times today, on oral contraceptives and weight gain. The post covers a review of various clinical trials (there are only three listed, but that's because they are using the most stringent measures of three treatment trials per study) and concludes that there is no causal association between oral contraceptive use and weight gain.
Yup. Again. Because this isn't news. In fact, it's a reprint of a review released in 2008. Combined oral contraceptives don't cause weight gain in any of the studies in which they've been tested.
I've seen studies like this before, and I commented on it to a female friend of mine. And I got the response I have now come to expect: "Well, I gained weight!"
Sci's gonna have to put on her ranty pants for a minute.
CORRELATION IS NOT CAUSATION. There are many reasons why one might gain weight about the time that one starts taking hormonal contraceptives. Examples of this include: moving off to college, beginning a different style of life, or simply growing older (aging is very correlated with weight gain, and I'm not talking getting up there in your 80's, I'm talking getting older than 12). There are many other reasons why a person starting on hormonal birth control might gain weight.
Why do people always blame the birth control?
My hypothesis is that the aura of hormonal contraceptives is to blame. The idea of putting outside hormones into your body is a scary one, and it's something that people feel they would notice. This may mean that women taking hormonal contraceptives are more on the lookout for changes in their bodies, and thus might notice (and attribute) weight that they gained at that time with the drugs they are taking. And there ARE side effects of hormonal contraceptives. Side effects on mood for some people, on headaches (either reduction or increase), or PMS symptoms (increase or decrease), on libido. Side effects on skin. Just not on WEIGHT.
It occurred to me today that, in this way, oral contraceptives have a thought process around them that is similar to stuff I've seen with things like homeopathy or vaccines and autism. No matter how many studies come out showing that homeopathy doesn't work/vaccines don't cause autism/hormonal contraceptives don't cause weight gain, the myth still perpetuates, and in fact seems to grow. The more studies the are announced about hormonal contraceptives having nothing to do with weight gain, the more people come out of the woodwork saying "But I gained weight! That study must be wrong!"
You may have gained weight. But (1) do you KNOW it was the contraceptive? Correlation is not causation. (2) You are an anecdote. And so are all your friends. You are not a controlled study evaluating the effects of hormonal contraceptives on weight gain. This doesn't mean you didn't gain weight, perhaps you did. It doesn't mean you didn't experience side effects from the hormonal contraceptive. Many people do. It just means that, on average, hormonal birth control alone does NOT cause weight gain.
In case you want references, here are some.
- Let's start with animals. No effect on weight or metabolic aspects in rats (these particular rats were rats with diabetes, but it confirms previous findings).
- No effect on weight in monkeys of normal weight, but this study actually saw a DECREASE in weight and fat composition in obese monkeys.
Now onward to humans.
- The most recent reprint of a 2008 review looking at three double-blinded clinical trials saw no differences in weight, and even looked at people who quit the studies, citing that they gained weight. Numbers of people quitting the study citing weight gain didn't differ between groups either, meaning that the numbers of people who thought they were gaining weight because of the contraceptive were as likely to be on placebo as not. They did see weight gain the progesterone only group getting the contraceptive as an injection. This study included the ring and the patch.
- People on combined oral contraceptives in this study gained less weight than those on placebo, and also gained less weight than those who discontinued usage.
- Oral contraceptives were associated with LESS weight gain and less fat than placebo in female distance runners.
- Another study looking at injectable progesterone vs oral contraceptives found that the oral contraceptive condition had no weight gain, though they did see weight gain with the injectable.
- Another study also found reduced fat mass for oral contraceptive users, with NO CHANGE in weight gain.
What can we conclude from this? We can conclude that combined hormonal contraceptives when given orally or as a patch or in the ring cause NO WEIGHT GAIN. What DOES cause weight gain is the progesterone only contraceptive, given as an injectable or as an IUD. Keep in mind, though, that the progesterone only contraceptive is actually not very common, the vast majority of women are on a combined hormonal contraceptive, usually oral, though patch and ring are gaining in popularity.
The other thing you can conclude from this? Weight gain happens. The oral contraceptive conditions in all the studies listed above (humans and animals) DID SHOW weight gain. But that's because EVERYONE showed weight gain. The people on oral contraceptives gained as much weight (or sometimes a little less) as those on placebos. So yes, you might gain weight when you go on an oral contraceptive. But so does everyone, including people NOT on the contraceptive.
To conclude: I believe you when you say you gained weight when you started on a hormonal contraceptive. But was it the contraceptive itself that was to blame? Probably not.
References (Lots of them! And these are only the ones I used. There are more.)
Uras R, Orrù M, Etzi R, Peppi G, Marotto MF, Pilloni M, Zedda P, Lello S, Melis GB, & Paoletti AM (2009). Evidence that in healthy young women, a six-cycle treatment with oral contraceptive containing 30 mcg of ethinylestradiol plus 2 mg of chlormadinone acetate reduces fat mass. Contraception, 79 (2), 117-21 PMID: 19135568
Berenson AB, & Rahman M (2009). Changes in weight, total fat, percent body fat, and central-to-peripheral fat ratio associated with injectable and oral contraceptive use. American journal of obstetrics and gynecology, 200 (3), 3290-8 PMID: 19254592
Beksinska ME, Smit JA, Kleinschmidt I, Milford C, & Farley TM (2010). Prospective study of weight change in new adolescent users of DMPA, NET-EN, COCs, nonusers and discontinuers of hormonal contraception. Contraception, 81 (1), 30-4 PMID: 20004270
Edelman, A., Jensen, J., Bulechowsky, M., & Cameron, J. (2010). Combined oral contraceptives and body weight: do oral contraceptives cause weight gain? A primate model Human Reproduction, 26 (2), 330-336 DOI: 10.1093/humrep/deq335
Adeghate E (2000). Effect of oral contraceptive steroid hormones on metabolic parameters of streptozotocin-induced diabetic rat. Contraception, 62 (6), 327-9 PMID: 11239621
Göretzlehner G, Waldmann-Rex S, & Schramm GA (2011). Extended Cycles with the Combined Oral Contraceptive Chlormadinone Acetate 2 mg/Ethinylestradiol 0.03 mg: Pooled Analysis of Data from Three Large-Scale, Non-Interventional, Observational Studies. Clinical drug investigation PMID: 21250761
Teepker M, Peters M, Kundermann B, Vedder H, Schepelmann K, & Lautenbacher S (2011). The effects of oral contraceptives on detection and pain thresholds as well as headache intensity during menstrual cycle in migraine. Headache, 51 (1), 92-104 PMID: 20946429
Breech LL, & Braverman PK (2010). Safety, efficacy, actions, and patient acceptability of drospirenone/ethinyl estradiol contraceptive pills in the treatment of premenstrual dysphoric disorder. International journal of women's health, 1, 85-95 PMID: 21072278
PROCTER-GRAY, E., COBB, K., CRAWFORD, S., BACHRACH, L., CHIRRA, A., SOWERS, M., GREENDALE, G., NIEVES, J., KENT, K., & KELSEY, J. (2008). Effect of Oral Contraceptives on Weight and Body Composition in Young Female Runners Medicine & Science in Sports & Exercise, 40 (7), 1205-1212 DOI: 10.1249/MSS.0b013e31816a0df6
Gallo MF, Lopez LM, Grimes DA, Schulz KF, & Helmerhorst FM (2008). Combination contraceptives: effects on weight. Cochrane database of systematic reviews (Online) (4) PMID: 18843652