Why Did I Gain Weight on the Pill, If the Research Says That Shouldn't Happen?

By Dr. Brooke Kalanick

GGS friend and fellow research rock star, Krista Rompolski, tackled the Truth About Birth Control and Weight Gain previously, presenting the various problems with the research (i.e. what constitutes “significant" weight gain) and how the type of hormone (estrogen or progesterone) in your birth control matters when it comes to weight gain and oral contraceptives.

In her article, Krista showed that at the end of the day the research is inconclusive. Dig into the scientific literature, and you will find that most studies show no correlation between the Pill and significant weight gain.

But I know there are many of you, myself included, who did have a very frustrating weight gain of anywhere between five and 15 pounds upon starting on the Pill. So, what gives? Are we crazy, or is this a case in which we have to look far deeper than what the available research tells us?

Well, of course, you’re not crazy, although you may have felt like it on the Pill—but that’s a subject for another day!

Why Some of Us Gain Weight on the Pill

Almost everyone tells us we shouldn’t have. Yet, we did. Why is that?

preventregain-buttonjeans-450x388It’s important to remember that hormones will behave different depending on the other hormones in your unique mix, so it’s very hard to look at just any one hormone in isolation—especially if you have any existing hormonal imbalance. The introduction of a bigger dose of any hormone will shift your already unbalanced scales, and you will likely experience more symptoms (you might even feel like the entire list of symptoms on the package insert is talking specifically about you). Most of what I’m about to discuss below goes beyond simply estrogen in the Pill causing weight gain. In this article, I’m diving a little deeper into the reasons why someone might experience more trouble with estrogen in the Pill.

Estrogen Dominance

I wrote about this sometimes vague and misunderstood term for GGS in the past (check out part one and part two of that series). If a woman is already estrogen dominant the Pill can easily make her even more so. This happens for a couple of reasons.

First, the Pill shuts off ovulation (that’s how it prevents pregnancy) so the woman doesn’t make the normal progesterone from the corpus luteum (the post ovulatory follicle that develops after an egg is released). The adrenals produce some progesterone, so depending on her stress level and adrenals status, she may fare worse than others with her adrenal progesterone back-up plan. Some pills also contain progesterone, and these seem to be associated with less weight gain.

When a woman becomes estrogen dominant, estrogen dominates progesterone and she loses some of the balancing effects progesterone has against the stress hormone cortisol, which can increase fat storage (especially around the midsection).

The more body fat a woman has, the more estrogen her body produces in that fat tissue. This happens through a process called aromatization, in which testosterone is converted to estrogen, quickly leading to an unfavorable hormone balance for fat loss: less testosterone and more estrogen. This process is turned on by blood sugar problems as insulin surges spur the aromatase enzyme.

Thyroid Effects

Estrogen and progesterone have some complex interactions with the thyroid. On the Pill a woman is at least relatively estrogen dominant and lower in progesterone (because her normal ovulation is disrupted). Here’s how that affects the thyroid:

Progesterone normally increases the TPO (thyroid peroxidase enzyme) production of thyroid hormone. A decrease or a lack of thyroid hormone can lead to hypothyroidism. Pills that include progesterone (that’s most of them these days) could theoretically lessen the impact, but synthetic progestins don’t seem to behave in quite the same way as our natural progesterone in all tissues.

Estrogen will increase thyroid binding protein, the protein carrier that shuttles around thyroid hormones, takes them to their target destination, and drops them off. When too much thyroid protein is bound up by proteins, there isn’t as much free or available for action (on lab tests this shows up as lower free T4, lower free T3, or lower T3Uptake). In short, having too much estrogen can make you a bit hypothyroid by decreasing your free, active, hormone.

Will every woman on the Pill end up with low enough T3 to feel the effects? Not necessarily. A lowering of free T3 will always happen with oral contraceptives to some degree, but if thyroid hormone levels are stellar, this may not be enough to cause hypothyroid symptoms like depression, fatigue, and weight gain. However, if thyroid hormone levels were already borderline or even overtly low, the Pill can easily push it low enough to produce symptoms.

Gut Microbe Effects

There’s so much we don’t yet understand about the increasingly complex effects our gut bacteria, or microbiome, has on our health and our hormones—but we do know it’s very important.

The research on the interactions between oral estrogens and the gut bacterial landscape is growing, and we now know a couple of things.

digestion101-gutbacteria-327x341Estrogens appear to alter gut bacteria. If you talk to any functional medicine practitioner, they’ll tell you that nearly all women who are taking estrogen have imbalanced gut bacteria. To me, this doesn’t necessarily prove that the Pill causes this disruption directly. It may be the low thyroid effect (thyroid hormone is key for proper gut health) or it may be that there’s more happening that we don’t totally understand yet.

We do know that oral estrogens have been linked in pre-menopausal women to an increased risks for Crohn’s Disease (an autoimmune, inflammatory bowel disorder). Estrogen is known to have some effects on the gut barrier (intestinal lining), thus it appears to have a role in the development of intestinal hyperpermeability and intestinal inflammation. Perhaps the cause is estrogen receptors present in the gut, or a disruption in the gut flora. Or perhaps estrogen can trigger autoimmunity (more on that in a moment).

We also know that gut bacteria have a role in metabolizing hormones, including estrogen. So a woman who has a disrupted intestinal balance already may have more trouble getting rid of excess estrogen. This can make her more estrogen dominant or lead to more estrogen related side effects of the Pill, or perhaps lead to the intestinal inflammation I just mentioned.

How does this affect weight gain? We looked at how estrogen dominance can increase weight, but we also know that a diverse, healthy intestinal landscape is key in health and weight loss. Studies are showing us that the less varied and healthy our gut bacteria is, the more inflammation, insulin resistance and weight gain we experience over time.

I’ve seen things written like “the Pill destroys your gut bacteria, just like antibiotics.” I think it is likely untrue and the research does not show it “wiping out” our flora in the same way antibiotics clear everything out. It’s more likely that it has a complex role with thyroid hormone, a woman’s genetic predisposition to inflammation and autoimmunity, and the current health of her gut bacteria (which honestly, as is the case with most of us, might need quite a bit of work!).

We have to remember that when it comes to hormones, it’s rarely so straightforward.

More often, it’s a “which came first” issue. For example, gut imbalance and inflammation can certainly create acne and altered hormones. If this the reason a woman went on the Pill was to clear up her skin, get her PMS under control, and get her period more regular, she is likely to also be one of the women with worse weight gain and symptoms on the Pill.


Surges in estrogen, like starting the Pill, going through perimenopause, or pregnancy have been shown to trigger autoimmune flares on the thyroid (probably other autoimmune disease affected here as well).

If a woman has a predisposition to autoimmunity, any surge in estrogen can be a cause in tripping it to turn on. Family history needs to be considered when it comes to initiating any type of oral estrogen and if she does have Hashimoto’s, it’s important to recognize that the Pill can trigger a flare.

Flares happen all the time, and one of my prime concerns in my practice is decreasing that frequency and lessening the tissue destruction. When there is an increased attack on the thyroid, a bit of tissue is destroyed and—you guessed it—it makes the woman more hypothyroid, this can impact weight loss. Many women will need an uptick in their thyroid hormone dose when they start the Pill . Others will go from not being on thyroid medicine to needing it.

Again, this won’t happen with every woman, but we know it happens, and it’s one more thread in a web that can lead to weight gain in some women when they take oral contraceptives.

Increased Appetite and Cravings

One reason for weight gain on the Pill may simply be increased calorie consumption. Estrogen and progesterone have complex interactions with leptin, ghrelin and neuropeptide Y—all of which can lead to feeling hungry. Female hormones also impact serotonin and GABA, brain chemicals that drive cravings. So it may be as simple as munching more overall, having a harder time getting satiated, or experiencing a shift in cravings and eating more sweets or starches.

Nutrient Deficiencies

It could be as simple as needing a multivitamin. The Pill creates a host of nutrient deficiencies including folic acid, B2, b6, B12, vitamin C, selenium, zinc, magnesium and vitamin E.

woman-taking-vitamins-450x300Many of us could shore up this problem with a high quality multivitamin/multimineral. However, if a deficiency already exists, gut issues are already present impacting absorption, and the woman is already depleted in nutrients that support hormone clearance by the liver, she of course would suffer from a host of symptoms related to nutrient deficiencies. This can include anxiety, depression, poor skin healing, low thyroid symptoms, anemias, etc.

What About Those Who Lost Weight on the Pill?

If a woman was low estrogen to begin with, the Pill may indeed help her lose fat. Estrogen is crucial for lean muscle mass and has an important role in fat burning. So if she were low, the Pill may have been a good addition to her fat loss hormone equation.

Women who may be low in estrogen include those who have PCOS (likely those who are not getting many periods, if any, in a year), and women going through perimenopause or who have premature ovarian failure (which is often autoimmune, but can also be due to disruption in the brain-ovary axis). Low estrogen can also be the result of chronic stress or thyroid disorders.

What to Do About Weight Gain If You’re on the Pill

Know yourself first.

What other issues do you have going on? These complex interactions can make you a better or worse candidate for the Pill.

Let’s say you have something like small intestinal bacterial overgrowth ( SIBO) or poor digestion, you don’t eat a lot of grains (i.e. following a low carb or Paleo diet, thus you may be low in B6), and you don’t take a multivitamin. Or you know that you have a MTHFR gene mutation impacting your folic acid status. You are likely going to have some trouble on the Pill. You won’t clear it well due to low B6 and folic acid, which affect a process called methylation. You will have altered liver clearance of the estrogens and will notice estrogen-dominant issues and possible weight gain.

Another scenario would be if you are borderline low T3 and start on the Pill, creating a selenium deficiency. Selenium is key for the conversion of T4 into the active thyroid hormone T3. Now you could easily be low enough T3 to suffer with low thyroid symptoms, and the Pill just tipped the scale enough for you to really feel the effect of it, including some weight gain. Remember that estrogen will also shift those levels of free T3 (the one you need), and together this may be enough to really push you into hypothyroidism.

See how quickly this gets complicated, and why you and your BFF won’t necessarily have the same response to the same pill? Or why the research is perhaps a little too lacking for these complex hormonal interactions you’ve got going on?

Where you start counts, too. If you’re already overweight, synthetic progestins in most pills seem to cause more weight gain. And if you did gain weight when you started taking the Pill, studies show you’re likely to keep gaining, or will have a hard time losing it. So the notion to “stick with it, and let it level out” doesn’t make sense in my experience (nor according some studies).

Finally, remember that the research repeatedly says that the Pill wasn’t associated with “significant weight gain.” That’s a bit subjective right? Two to three pounds will feel different to different women. And because it’s so complex, think about this: if you put on three pounds due to your response to the synthetic progestin, three pounds from your sluggish thyroid and two pounds from estrogen dominance related issues that’s now eight pounds. That may very well feel “significant”.

Next, trust yourself.

I love research. It is how medicine works, and that’s a good thing—but it’s not the only thing. We have to let each woman take a look at her bigger hormonal picture and see what makes sense for her. By all means, don’t ignore yourself because the data implies that what’s happening with you shouldn’t be happening, or because someone tells you it’s all in your head (argh, do I ever hate that line!).

The Pill isn’t evil but it’s also not benign.

Your hormonal balance is beautifully and insanely complex. Taking a hormone has profound and complex interactions throughout your body, from your brain to your gut.

Women with less complex issues will obviously do better when introducing the Pill. If you have hormonal imbalances already, it’s more likely to make those imbalances worse, it really doesn’t correct anything (besides low estrogen for some). It does have some clear upsides like great skin, a regular, predictable (and usually pretty light) cycle—and for some women with low estrogen, it can help with weight loss.

However, if you’re considering the Pill for other reason like acne, PMS, irregular or heavy cycles, the Pill is at best a band-aid and will make many hormonal issues (like PCOS) worse when you come off it. There are so many ways to get your bleeding, mood, cycle, and breakouts under control and actually fix or substantially correct your hormonal imbalances, rather than cover them up or stress your system more.

If contraception is not the reason, find out how to get to your root cause and start setting your hormones straight, clearing up your skin and getting your period under control. The Pill isn’t necessarily the wrong choice for every woman, but know that it’s not the only choice.

Um... Dr. Brooke, what about preventing pregnancy?

One thing we can’t argue with is that the Pill is a relatively convenient and very reliable way to avoid getting pregnant.

There are non-hormonal methods of contraception that range from not having to think about it at all (i.e. the non-hormone IUD Paraguard, not the ones which secretes hormone), to the ol’ standbys like the diaphragm, cervical cap, and condoms that require more thought and planning in the heat of the moment.

Not every woman will tolerate an IUD (some experience cramping and heavy bleeding), but if it works for you, it’s a great option. Again, I’m talking non-hormonal IUD here (i.e. the Paraguard). The others involve a little planning and some spermicide (again, not something every woman tolerates), but they don’t mess with your hormones. And let’s never forget, it’s OK to ask your partner to be in on the birth control conversation.

So many couples I talk to are certain they do not want children and need a reliable contraceptive method, but haven’t discussed vasectomy. It’s quick, fairly painless (I know a man might disagree, but let’s talk after he gives birth), and more easily reversible than tubal ligation or tubal coils (Essure), should anyone have a change of heart about having kids. Men are often a little skittish, understandably so, but it’s a very good option for many couples and no one’s hormones get mucked with.

Ah, the Pill and weight gain….not so simple, huh?

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About the author:  Dr. Brooke Kalanick

Dr. Brooke Kalanick earned her Doctorate in Naturopathic Medicine from Bastyr University. Known as “The Hormone Whisperer,” Brooke's balanced approach to health, using both conventional and alternative therapies, allows her to successfully treat patients with Hashimoto’s Hypothyroidism and PCOS as well as other female hormone imbalances. Learn more about Dr. Brooke on her website and connect with her on Facebook and Twitter.

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