This post was updated on December 19th, 2021

Metformin is one of the most commonly prescribed treatments for women with polycystic ovary syndrome (PCOS), but it’s not actually approved for this purpose, even if you’re pre-diabetic. There are good reasons for this as according to the latest scientific reviews, metformin is no longer considered a helpful drug if you’re trying to lose weight or get pregnant.

Let me explain.

In 2003 Dr Robert Barbieri, a highly cited leader in the field of Obstetrics, Gynecology and Reproductive Biology authored a guide to his colleagues on the use of metformin for the treatment of PCOS (Barbieri 20031). 15 years later, along with many other experts in the field, he is now saying that metformin should not be used for any indication as a first-line therapy for women with PCOS (Barbieri et al. 20182).

So why the change of heart?

Like all good scientists, it appears that Dr Barbieri updated his views as better information became available.

Given these latest recommendations, it appears from metformin’s continued use in treating PCOS, that as a community, we’re falling victim to a lengthy lag time between research findings and clinical practice (Morris et al. 20113). This a well understood problem that’s both affected me personally, as well as thousands of other women I meet during my free 30 Day PCOS Diet Challenge.

Many of the women I speak to during this live event have been given this drug either to help them lose weight, to lower the risk of type 2 diabetes, or to help them get pregnant. As you’re about to discover though, there are far better solutions to all of these problems that also happen to be free from the side effects of this outdated drug.

So without further ado, here’s five reasons not to take metformin for PCOS.

1. The Metformin Weight Loss PCOS Myth

I love shopping at IKEA, but I always get my husband to assemble the parts. I’ve tried doing it myself in the past, but I get to the first picture where it shows the guy with the frowny face and the big question mark and I’m done.

Way too confusing!

So I’ll admit, there’s a lot of simple stuff that confuses the heck out of me, but understanding how metformin affects body weight isn’t one of them.

Metformin For PCOSIt’s clear from the latest systematic reviews that metformin doesn’t help with weight loss and only causes slight improvements in where your excess body fat is located (Morley et al. 20174). By looking only at a few isolated studies, it would be easy to come to a different conclusion. For example, some smaller (and older) metformin weight loss PCOS studies show a slight benefit from this drug. But the size of the effect is always small and is easily overshadowed by other interventions – especially dietary change (Nieuwenhuis-Ruifrok et al. 20095).

This is where meta-analyses are the best source of information because they combine the results from all relevant studies to see the overall affect. Any conclusions that can be drawn are the most scientifically robust. In the 2017 analysis by Morley and colleagues, which compared metformin therapy in women with PCOS with no treatment at all, there was a tiny improvement in waist to hip ratio, but the effect on body weight was nothing… zilch!

If there was one paper on metformin and PCOS that I wish doctors would read, this would be it. The 2018 analysis and updated recommendations by Drs Barbieri and Erhrmann I mentioned at the top of the article would come a close second as in it they specifically say that “metformin does not produce enough weight loss to qualify as a weight loss drug”. So many women are incorrectly prescribed metformin to help them lose weight, when the information available shows that it doesn’t actually help.

If you’re taking metformin for PCOS and were hoping to lose some weight, don’t let this news get you down. While this particular drug is clearly not the answer you’re looking for, the scientific community has shown us where to find a more comprehensive solution. One that targets the root problem of PCOS weight gain instead of using band-aid solutions like metformin.

Metformin For PCOS

Out of all the studies that explain the root cause of PCOS, the best one I’ve read to date is a double-blinded randomized controlled trial (the gold standard of high-quality research) conducted in 2012 by Indiana University and the Mayo Clinic (Gonzalez et al. 20126).

In this well-designed experiment, researchers took lean and otherwise healthy women, and effectively “gave them” PCOS for five days (I know… thanks for nothing right?). They did this by giving them the androgenic “male” sex hormones that are typically elevated in women with PCOS. What they showed was that these elevated androgens caused unhealthy changes to the subjects’ blood glucose regulation, just like in women with real PCOS. These previously healthy, uninflamed women had an increase in inflammatory biomarkers after taking the PCOS androgens, but it was the consumption of glucose that caused the inflammation to take off. Remember that these were lean women with healthy levels of body fat.

What this tells us is that elevated androgens and diet-induced inflammation lie at the root cause of our PCOS symptoms independent of bodyweight. It also tells us that insulin resistance and subsequent weight gain are secondary effects caused by these underlying mechanisms (Gonzalez 20127).

As well as showing that metformin is not equipped to address the root cause of your insulin problems (see reason #2), this high-quality study also hints at the most effective way to lose weight with PCOS. Reducing inflammation through the foods you eat targets the root cause of your PCOS symptoms, including that stomach fat that just won’t budge.

While things like exercise, sleep, and stress management can help too, what you eat is by far the most important step.

Here are a couple of real-life examples that illustrate just how powerful dietary change can be for weight loss, even for some of the hardest PCOS cases.

When I first met Kendall, back in 2016, she was at the end of her tether after having gained a lot of weight in a few short years. At 260-odd pounds, she was determined to do whatever it took to get back to a healthy body weight. By sticking with the dietary fundamentals she learned during my free 30 Day PCOS Diet Challenge, Kendall began eating a low inflammation diet that treated her PCOS at the roots. She stuck with it and lost 100 pounds over the next three years, while at the same time eliminating all of her other PCOS symptoms.

Kendall didn’t take medication to achieve this feat, nor did she do any crazy dieting. She simply modified what she ate in line with evidence-based nutritional principles for women with PCOS.

Another previous Challenge participant, Karina K, had been battling with her weight for most her life. She also struggled with acne, low energy, and a temperamental mood – particularly in the evening when her sugar cravings were bad. During my free 30 Day PCOS Diet Challenge Karina was able to lose 12 pounds by sticking to the PCOS diet principles I outline here.

She was motivated by these early results so kept on going in the following months. Karina’s acne cleared up, her mood improved, and her energy levels went through the roof. She was able to sustain the positive changes she was making and within nine months she had reached her goal weight after losing more than 60 pounds. She didn’t need drugs, supplements, or meal replacement shakes. Just good old-fashioned healthy whole foods eaten in a way that paid respect to her diagnosis.

You can read Karina’s full story, told in her own words here.

2. Metformin And PCOS: A Band-Aid Solution For Type 2 Diabetes

Back in the day when I was young and living on the cheap near the beach, I’d surf for days on a dinged-up surfboard that I’d “repaired” with duct tape. While I was (and still am) totally happy to patch up a hole in the rail so I can stay out in the water longer, I don’t recommend you take this approach for managing insulin resistance.

Unfortunately, this is exactly what’s happening when you use metformin to prevent diabetes.

As a proven insulin sensitizer, you’ll get no argument from me that metformin can reduce the chances of insulin resistance turning into full-blown type 2 diabetes. This is one of the most common answers we’re given when we ask our doctors, “so what does metformin do for PCOS again?” But this solution is a lot like saying my duct tape ding repairs make my board as good as new. In both cases, we’re failing to address the root cause of the problem.

Metformin For PCOS

As I mentioned above, in women with PCOS, insulin resistance is caused by a combination of our elevated androgens and the wrong kind of diet for our condition. Sure, there are definitely genetic and environmental factors that created this problem in the first place, but once you’re stuck with PCOS, then diet is the only causal mechanism you can actually do something about. This is why even if you’re eating “relatively healthy”, unless you’re specifically addressing diet-induced inflammation then you’re not going to regain control of your PCOS symptoms.

Because it only targets the secondary problem of insulin sensitivity, while making no difference to what you’re actually eating, metformin is the quintessential band-aid PCOS solution.

The research says so too.

In an impressive study conducted by the Diabetes Prevention Program Research Group, 3234 people at risk for developing diabetes were assigned to either metformin therapy or an intensive, 24-week program focusing on diet and exercise (the lifestyle intervention group).

During a mean follow-up period of 2.8 years, metformin reduced the incidence of newly developed diabetes cases by 31% while people that had focused solely on their diet and exercise behavior reduced their risk by 58% (Knowler et al. 20028). There are two conclusions that can be drawn from this data. Firstly, to be fair, the benefits of metformin for PCOS can be seen in the 31% risk reduction compared to the control group who only received a placebo pill.

What’s of much more value however is that when compared to people that took metformin, the risk of diabetes halved for people who focused solely on eating better and doing more exercise.

Metformin For PCOSIt was also found in the drug arm of this trial that the majority of the benefit achieved by metformin did not persist when the treatment was stopped (Knowler et al. 20039). Metformin only works as long as you’re taking it, which is great for Big Pharma, but not so good for you…

This study clearly illustrates the benefits of dietary intervention over metformin for diabetes prevention. And that’s saying nothing about the negative side effects of this drug which I discuss more below.

While these results driven studies give us the right answer, to understand why the right diet works so well, we need to look at the mechanisms involved. This is why I love the study by Gonzalez and colleagues so much (see Reason #1 above). As we now know from this high-quality study and others like it, insulin resistance is caused by inflammatory processes that are primarily triggered by the foods you eat.

This means we can fight this disorder at the root cause both by avoiding pro-inflammatory foods and by eating more of the things that are rich in antioxidants. We can also take things a step further and restore our insulin sensitivity by giving our cells a break from spikes in our blood glucose levels.

We do this by being smart about carbs and the other foods we eat.

Using this approach, me and hundreds of other women I’ve met through my free 30 Day PCOS Diet Challenge have actually been able to reverse their insulin resistance and get their sensitivity back to normal. The ability of our body to heal itself despite years of mistreatment really is something to behold.

Here’s a couple of great examples you might find interesting.

Lisa Hiebner was diagnosed with PCOS and insulin resistance back in December 2017. As is still so common, her doctor put her on metformin and sent her on her way. Feeling deflated, she jumped on google that night where she read about my PCOS dietary recommendations and signed up for my free Challenge. Lisa committed to tightening up her diet by eliminating sugar, dairy, gluten, and soy from her meals.

Two months after she was given her prescription, Lisa had to stop taking metformin because it was constantly making her sick to the point where she was barely able to eat. While her doctor told her it would be a waste of time rechecking her blood work, when she retested in November 2018, not only had her insulin sensitivity returned to normal, but so too had her hormone levels, thyroid function, and previous vitamin deficiencies. This was all without the help of medication.

Lisa gave me permission to include her good news here which she posted in my PCOS Support Facebook Group not long after getting her test results back.

Valerie Williamson was another classic high-risk candidate for type II diabetes that altered her future by following a PCOS friendly diet. When she signed up for my Challenge, on top of her PCOS, she was also facing insulin resistance which was particularly scary given her mom had recently been diagnosed with diabetes. But Valerie was determined to find a better path for herself. After six months of following my dietary principles, she was able to go off metformin entirely. After another six months had past, Valerie posted this wonderful message in our Facebook Group which she has kindly let me include here.

3. Metformin Does Not Help With PCOS Infertility

As someone that spent over five years trying to get pregnant, I’m no stranger to that fearful feeling that comes when you contemplate a future without children. No matter how hard I worked to distract myself, infertility was a cloud that hung over me which grew darker and darker with every year that passed. I eventually worked my way up the fertility treatment escalator but none of the conventional interventions worked – including metformin.

Metformin For PCOSAs I have since learned, infertility is the second biggest reason women with PCOS are prescribed metformin, so I’m definitely not alone in being disappointed by this drug. Looking back now, I wish I’d known more about the efficacy of this treatment option before I wasted so many precious months trying it.

While there are plenty of older studies that show metformin improves menstrual frequency, ovulation, and clinical pregnancy rates in women with PCOS, the most salient finding is that these benefits don’t actually result in more babies being born (Tang et al. 201210 – see footnote 1). If this sounds confusing then you’re not the only one, as it took me some time to get my head around this one too.

It seems that metformin has the ability to increase pregnancy rates, but these extra pregnancies are unlikely to be carried to term. Having lived through a couple of miscarriages myself I can say with full confidence that this sucks big-time. To me anyway, this is another example of metformin being inappropriately prescribed when the science is pretty clear that it’s not the best solution.

It’s unfortunate that this news is taking so long to reach clinical practice as even the Endocrine Society Clinical Practice Guidelines state that “…metformin is beneficial for improving menstrual irregularities, but it has limited or no benefit in treating hirsutism, acne, or infertility.” (Legro et al. 201311).

Metformin For PCOS

Possibly of most importance to anyone trying to conceive though, is the fact that in addition to not increasing your chances of success, metformin can actually be harmful to your fertility because it depletes your vitamin B12 levels (Aroda et al. 201612). You may have heard that folate (vitamin B9) is important during pregnancy, but B12 is just as essential to avoid a range of unnecessary metformin PCOS pregnancy risks. These include increased chances of preterm birth/reduced birth weight (Rogne et al. 201713); and a 2-4 fold increased risk of your baby developing neural tube defects like spina bifida (O’Leary et al. 201014).

Despite this shortcoming, many doctors still don’t make a habit of checking PCOS patients’ B12 levels, let alone prescribing a supplement.

Changing my diet enabled me to finally fall pregnant naturally after everything else had failed. It’s because of this experience that I love more than anything seeing the same thing happen to others. Bianca K and Jamie Bietzell are two great examples that warm my heart whenever I think of them.

Thanks to her PCOS diagnosis, Bianca had struggled with her weight all her life and was told she needed to get things under control if she wanted to have a healthy baby. She had tried metformin but to no avail and her desperation led her to eventually make an appointment for bariatric surgery. After joining my free 30 Day PCOS Diet Challenge in 2016, Bianca ended up cancelling her appointment because she had started losing weight for the first time ever. She went off all medications and lost 30 pounds over the next few months. While our PCOS community celebrated this success with her, Bianca finally got what she really wished for when she fell pregnant naturally and had a healthy, happy pregnancy.

You can read a full account of Bianca’s journey to motherhood here.

Jamie Bietzell is another great example of both the false hope of metformin, as well as the jaw-dropping results of treating PCOS infertility through dietary changes. After a lifelong battle with her weight, four years of heart-wrenching infertility, and two years of metformin side effects, Jamie decided enough was enough.

In November 2017 she took part in my free 30 Day PCOS Diet Challenge and started applying everything she learned. By January of 2018 she was getting a regular cycle, and by April she had lost 50 pounds. She went from a size 22 jean to a size 18, her A1C levels fell out of the diabetic range, and her blood pressure measurements showed she was no longer hypertensive. My favorite bit of this story though is that by November 2018 Jamie was 30 weeks pregnant. No supplements, no drugs, just the right type of food.

You can read her full story here.

4. Many Women With PCOS Can’t Handle Metformin Side Effects

In my experience, women with PCOS tend to be a pretty resilient bunch. Living with this disorder can be hard on our self-confidence, and we’re often doing battle with stress, anxiety, and depression as a result of our diagnosis. But we punch-on right, ‘cause that’s what we do.

But while I definitely think that we’re tougher than most, even women with PCOS find the metformin side effects pretty intolerable.

In addition to the fact that it causes a vitamin B12 depletion (Aroda et al. 201612), the most widely reported side effects are “gastrointestinal discomfort”. This is the polite way of saying it makes you want to puke, and gives you terrible diarrhea.

Not wanting to rely on just my own bad experience with this drug, I thought it worth enquiring within my PCOS support Facebook Group. When I polled the group, out of 1300+ responses, 78% of respondents reported adverse side effects. These included diarrhea, heartburn, nausea, abdominal pain, bloating, and retching.

Metformin For PCOSHere are some of their comments:

“I was violently sick and couldn’t eat, everyone thought I had morning sickness so I had to stop taking it.”

“It made me super sick and it was a terrible experience.”

“I was always sick to my stomach on it.”

“I had numerous side effects, tiredness, nauseous, headaches, pain in my abdomen.”

“The metformin I started taking for fertility made me bleed for over 20 days and I had to go to urgent care due to anemia.”

When considering metformin side effects it’s also worth noting that while it appears to be a rare risk, there have been multiple case study reports of metformin causing liver injury (Zheng et al. 201615; Saadi et al. 201319; Hashmi 201120). Given the elevated risk of liver disease that comes with having a PCOS diagnosis (Kelley et al. 201416), this is something I think everyone should be warned about.

I thought it also worth mentioning that due to its various adverse effects, rodent studies suggest that metformin may increase the risk of Alzheimer’s disease (Picone et al. 201617).

So while metformin may widely be considered a “safe” drug, it’s definitely not without its risks.

5. There Is A Much Better Alternative To Metformin For PCOS

The final nail in the metformin coffin is the fact that there’s a much better solution without any side effects.

Metformin For PCOSWithout wanting to sound like a broken record, the truth of the matter is that dietary intervention is the best way to address the root cause of insulin resistance and the hormone dysregulation of a PCOS diagnosis.

Just like how fire depends on three things: oxygen, an ignition source, and fuel to burn, our PCOS relies on elevated androgens, chronic inflammation, and certain kinds of foods to sustain itself. There’s not much we can do about our genetics or the environmental conditions that gave rise to our diagnosis. But by eating an anti-inflammatory diet, our PCOS problems will burn themselves out.

While other lifestyle interventions like exercise, sleep, and better stress management can make a big difference too, these won’t give you the results you need until you’ve got the diet thing happening first.

Let me give you one last success story to really drive this point home.

Alisha P had been struggling to fall pregnant for two years after going off birth control pills. Her OB, and fertility specialist suggested taking clomid, while her endocrinologist recommended metformin. Alisha knew there had to be a better way so she politely declined both of these drugs, and went searching for a different option.

After finding my website and taking part in my Beat PCOS 10 Week Program, Alisha learned what a balanced, PCOS friendly diet really looked like and started making more time to create healthy meals.

Within a few months of these dietary changes she went from having no energy to having tons of energy. She lost 30 pounds, and started feeling great about herself. Her skin cleared up, her hormone blood tests came back normal, and her previously absent periods returned to a regular cycle. But the best part was that within only three months of embracing a PCOS friendly diet Alisha was able to fall pregnant naturally – just the way she had always hoped for.

Alisha is a bright and caring woman, who has kindly shared more of her story here along with some of the practical things that helped her achieve these extraordinary results.

Lastly, I know that one of the biggest fears for anyone that’s been on metformin for years, is that they’ll put on weight if they stop. I don’t want to sound cavalier about this genuine concern, but a better understanding of how metformin works can help you mitigate this risk completely.

The best information we have to date suggests that metformin’s insulin sensitizing action stems largely from its anti-inflammatory and anti-oxidant properties (Dehkordi et al. 201918). The good news is that we can achieve a similar result by eating the right PCOS diet. A wholefoods-based diet that is rich in vegetables, that also happens to avoid pro-inflammatory foods like sugar, refined carbohydrates, vegetable oils, gluten, and dairy, will provide you with all the support you should need.

When used correctly, food really can be medicine – and it tastes a lot better than a gelatin capsule.

In my opinion, metformin for PCOS is a half-baked solution that even the experts are now starting to walk away from. So why settle for a second, or even a third-rate solution especially given the adverse effects? You deserve better, and whether you’re trying to lose weight, manage your insulin levels, or get pregnant, if PCOS is the problem then there is a much better option.

If you’re open to giving my dietary approach a chance, then here are some free resources to help get you started. If you want to begin eating a PCOS friendly diet today but don’t know where to start, I suggest downloading this free 3 Day PCOS Meal Plan. I also recommend sticking a copy of this PCOS Diet Cheat Sheet on your refrigerator door and trying not to eat the foods on this PCOS Foods to Avoid Checklist.

For the most immersive experience though, I hope you’ll come join me for my next 30 Day PCOS Diet Challenge. I run this free program four times a year so chances are we’re either doing one right now, or we’ll be starting one soon.

In good health,

xo Kym



Footnote 1: The Cochrane systematic review by Tang et al. 2012 was superseded in 2017. Unlike the earlier review, the updated analysis concluded that metformin slightly improves live birth rates. This different result was due to the inclusion of a single additional study however the statistical certainty of this updated finding remains very weak. As the authors of the 2017 review note, “… there are still only four studies reporting live birth available for analysis, and the overall quality of the evidence is low. Given the wide-ranging confidence intervals and evidence quality, the advantage offered by metformin remains difficult to interpret clinically.” What they’re saying is that they’d be nervous to make treatment recommendations based on this evidence.

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