If you've ever Googled your symptoms at midnight — the irregular periods, the pain, the bloating that makes you look six months pregnant by 3pm — you've probably ended up down a rabbit hole comparing endometriosis vs PCOS. And if you're anything like me, you came out more confused than when you started. Here's the thing that took me years to understand: these are two completely different conditions. Different mechanisms, different tissue, different hormonal profiles. But they share enough symptoms that they get mixed up constantly — by patients, by GPs, and sometimes, honestly, by gynaes who aren't specialists in either. I was misdiagnosed with IBS and anxiety for seven years before anyone mentioned endometriosis. A lot of people I know in the endo community were told they had PCOS first. Some of them actually do have both — which, as you can imagine, is its own particular kind of complicated. This article isn't going to be a textbook comparison. What it's going to do is explain, as clearly as I can, what makes these conditions different, where they genuinely overlap, why getting the right diagnosis matters more than you might think, and what the research — limited and messy as it sometimes is — actually tells us about having one or both. If your gyn has been vague, if you've been handed a diagnosis that doesn't quite fit, or if you're just trying to understand your own body better: this is for you.
What We're Actually Talking About
Let's start with the basics, because I think a lot of the confusion comes from people using these terms interchangeably when they describe completely different things happening in the body. Endometriosis is a condition where tissue similar to the lining of the uterus grows outside the uterus — on the ovaries, the bowel, the bladder, the peritoneum, sometimes further. This tissue responds to hormonal cycles the way the uterine lining does: it swells, breaks down, but has nowhere to go. The result is inflammation, scarring, and adhesions. That's the short version. The lived version is: the pain that wakes you up at 2am, the period that puts you on the bathroom floor, the bowel symptoms that got you referred to a gastroenterologist for three years before anyone looked further. Polycystic ovary syndrome (PCOS) is a hormonal and metabolic condition. The name is a bit misleading — the "cysts" are actually small follicles that haven't matured and released an egg properly. PCOS is typically characterised by irregular or absent ovulation, elevated androgens (male hormones like testosterone), and often — though not always — polycystic-appearing ovaries on ultrasound. The symptoms can include irregular periods, acne, excess hair growth, weight changes, and fertility challenges. Different mechanisms. Different tissue. Different hormonal fingerprints. What they share: both can cause irregular periods, both can affect fertility, both are frequently dismissed or misdiagnosed, and both disproportionately affect people who spend years being told their symptoms are normal.
Why They Get Confused
The symptom overlap is real, and it's worth naming specifically. Both conditions can cause: - Irregular or painful periods
- Bloating and digestive disruption
- Fatigue that doesn't respond to sleep
- Difficulty getting pregnant
- Pelvic pain (though the character and timing differs) The difference is often in the type of pain and the hormonal profile. Endo pain is typically cyclical but can become chronic — it often peaks around ovulation and menstruation, and is frequently described as deep, stabbing, or burning. PCOS pain, when it occurs, tends to be more related to ovarian cysts or the pressure of multiple follicles. The other issue is that standard blood tests and even standard ultrasounds don't reliably diagnose endo. A GP looking at your bloods might see hormonal irregularities that point toward PCOS, while the endometriotic lesions quietly do their thing elsewhere. A general gynae doing a pelvic ultrasound might miss endo entirely — especially if it's not on the ovaries in an obvious way — and flag the polycystic appearance of the ovaries instead. This is not a hypothetical scenario. It's what happens to a lot of people.
The Hormonal Picture
This is where things get genuinely interesting, and also genuinely complicated. PCOS is fundamentally a hormonal condition. Elevated LH (luteinising hormone), elevated androgens, often elevated insulin — these are the markers that help diagnose it. The hormonal environment in PCOS is typically androgenic (high testosterone-adjacent hormones), which suppresses regular ovulation. Endo, on the other hand, is often described as an oestrogen-dependent condition. The lesions are driven and sustained by oestrogen. Many treatments for endo work by suppressing oestrogen — hormonal contraceptives, GnRH agonists, newer medications like Ryeqo (relugolix). This is almost the opposite hormonal profile to PCOS. So in theory, you'd expect these conditions to be mutually exclusive. In practice, they're not. Anti-Müllerian hormone (AMH) is one marker that comes up in both contexts. AMH is produced by granulosa cells in growing follicles and is used as a measure of ovarian reserve — essentially, how many viable follicles remain 2. In PCOS, AMH is often elevated, because there are many small follicles producing it. In endo, particularly when it affects the ovaries (endometriomas), AMH can be reduced — surgery on ovarian endometriomas can further deplete it. This matters enormously for anyone thinking about fertility. A high AMH in PCOS doesn't straightforwardly mean "good fertility" — it means lots of follicles that aren't ovulating properly. A low AMH from endo-related ovarian damage means a reduced egg pool. If you have both, the picture is even harder to interpret.
When You Have Both
Yes, this happens. It's not common, but it's not rare either. A 2024 population database study 3 looked specifically at pregnancy and delivery outcomes in women who had both PCOS and endo, compared to women with PCOS alone. The researchers described both conditions as
— and found that having both together creates its own distinct risk profile that isn't simply the sum of two separate conditions. The study was retrospective and used ICD-9 coding from a US hospital database, which means it has real limitations — coding accuracy, selection bias, the fact that many endo diagnoses are missed or delayed. But it's one of the few studies that has tried to look at this co-occurrence directly, and it's a start. What does co-occurrence look like clinically?PCOS and endometriosis are independent risk factors for perinatal outcomes.
Ismail S, Majdell C, Badgheish A, et al. — Pregnancy, delivery, and neonatal outcomes among women with PCOS and endometriosis: a population database cohort. Archives of gynecology and obstetrics, 2024. View paper →
Often: difficult, delayed diagnosis. A PCOS diagnosis that explains some symptoms but not the pain. Or an endo diagnosis that explains the pain but not the irregular cycles. Or — and this is the one that makes me frustrated on behalf of everyone who's been through it — a gyn who treats one condition and never thinks to look for the other.
Diagnosis:
Why It's Not Simple Diagnosing PCOS is done clinically, using the Rotterdam criteria: you need two out of three — irregular or absent ovulation, elevated androgens (on bloods or clinical signs), and polycystic ovarian morphology on ultrasound. No surgery required. Diagnosing endo definitively still requires a laparoscopy — a surgical procedure — with histological confirmation of the tissue. A lap with no endo found, performed by a general gynae rather than an endo specialist, does not necessarily mean no endo. This is something the community talks about constantly, and it's not paranoia: skill, surgical experience, and equipment all affect what gets found. Ultrasound is increasingly being used to detect endo — particularly deep infiltrating endo and ovarian endometriomas — when performed by a trained specialist. AI-assisted ultrasound analysis is an emerging area of research 1, though it's not yet standard clinical practice. For PCOS, ultrasound remains a key diagnostic tool, looking at follicle number and ovarian volume. The point is: these are different diagnostic pathways, and conflating them leads to people being misdiagnosed, under-investigated, or treated for the wrong thing.
What the research actually says
What the Research Actually
Shows I want to be honest with you about the state of the evidence here, because I think people with endo (and PCOS) deserve that honesty rather than false certainty. The research on endo vs PCOS as separate conditions is reasonably solid. We know they have different mechanisms, different hormonal profiles, different tissue involvement. That part isn't controversial. The research on co-occurrence is thin. The 2024 study by Ismail et al. 3 is one of the few that has tried to quantify what happens when someone has both. They found that — and that the combination creates specific risks during pregnancy and delivery that haven't been well-studied at a population level. The study group (women with both conditions) numbered only 163, compared to 14,719 in the PCOS-only group. That's a small number, and it reflects how rarely co-occurrence has been captured — or perhaps how often it's been missed. On AMH as a diagnostic and prognostic marker: the research 2 shows it's a genuinely useful tool for understanding ovarian reserve, and that it behaves differently in PCOS (elevated) versus endo-related ovarian damage (reduced). But AMH interpretation is context-dependent. A number on its own doesn't tell the whole story, and I'd be cautious about anyone presenting a single AMH result as. On ultrasound and diagnosis:
AI-assisted ultrasound analysis is being studied for both conditions 1, and the field is moving, but it's not yet a replacement for specialist clinical assessment. The research is still being synthesised and evaluated. What we genuinely don't know well: the exact prevalence of co-occurrence, the best treatment approach when someone has both, and whether treating one condition affects the course of the other. The research is mixed, and in some areas, it's just sparse. This is gonna sound dramatic, but — we're still in a situation where conditions that affect millions of people are dramatically under-researched. That's not a medical opinion, that's a fact about where funding and attention have historically gone.
What to do with this
What This Actually Means for You
If you're trying to figure out whether you have one, the other, or both — here's what I'd suggest thinking about, based on everything I've read and lived. Track the type and timing of your pain. Endo pain is often cyclical and tied to your menstrual cycle — but it can also become constant over time. PCOS is less consistently painful, though it can cause pelvic discomfort. A symptom diary isn't glamorous, but it gives you something concrete to bring to appointments. Push for the right bloodwork. For PCOS, you want LH, FSH, total and free testosterone, SHBG, AMH, and often fasting insulin. For endo, there's no reliable blood test — but CA-125 is sometimes checked, with the caveat that it's not specific to endo and has major limitations. Don't let a "normal" blood panel tell you your pain isn't real. Ask specifically about ultrasound expertise. If you're being investigated for endo, ask whether the person doing your ultrasound has specific experience in looking for deep infiltrating endo and endometriomas. This matters. A standard pelvic ultrasound by someone without that training will miss a lot. If you've been diagnosed with PCOS and the pain doesn't fit, say so. A PCOS diagnosis doesn't rule out endo. If your pain is severe, cyclical, or affecting your bowel or bladder, that warrants further investigation — ideally with an endo specialist, not just a general gynae. If you're thinking about fertility, and you have either or both conditions, ask specifically about your AMH and what it means in your context. The interpretation is different for PCOS versus endo-related ovarian damage 2. And if you've had a lap that came back clear but your instincts are telling you something is still wrong: that feeling is worth pursuing. A negative lap by a general gynae isn't the same as a negative lap by a specialist.
Bottom line
Endometriosis and PCOS are distinct conditions with different mechanisms, different hormonal profiles, and different diagnostic pathways — but they share enough symptoms that confusion and misdiagnosis are genuinely common. They can co-exist, and when they do, the combined picture is more complicated than either alone 3. Getting the right diagnosis — or diagnoses — matters because the treatments are different, the fertility implications are different, and managing one without knowing about the other means you're working with incomplete information. The research on co-occurrence is still thin, and we don't have all the answers yet. One specific thing you can do today: write down your symptoms — the type of pain, when it happens, what makes it worse, what it stops you doing — and bring that list to your next appointment. It's not a dramatic action, but it's a concrete one, and it changes the conversation.