Endometriosis vs Adenomyosis: A Side-by-Side Guide

If you've spent any time in endo forums — or sitting in a waiting room clutching a printout you found at midnight — you've probably seen both words: endometriosis and adenomyosis. Maybe your gyn mentioned one and you went home and fell down a research hole. Maybe you've been diagnosed with both, which is more common than most people realise, and you're trying to figure out what that actually means for your body. Or maybe you've just been told you have "a uterine condition" and you're trying to work out which one, because the symptoms overlap in ways that feel almost cruel. Here's the thing — these two conditions are related but genuinely different. Different tissue, different location, different mechanisms, different ways they mess with your life. And yet they share so much: the pain that doesn't match what anyone prepared you for, the heavy bleeding, the fertility questions, the feeling that something is deeply wrong that took years to be believed. This article isn't going to give you a textbook comparison. It's going to tell you what actually differs — the symptoms, the diagnosis, the treatment paths — in language that's useful when you're trying to understand your own body. We'll cover what each condition is at a tissue level, how the symptoms overlap and where they diverge, what the research says about having both at once, and what all of this means practically if you're a diagnosis or still trying to get one.

What's actually happening in each condition

Let's start with the biology, because it matters — not in a textbook way, but in a "this is why my pain feels like this" way. Endometriosis is when tissue similar to the lining of the uterus grows outside the uterus. On the ovaries, the bowel, the bladder, the peritoneum, the ligaments. Sometimes further — there are documented cases on the diaphragm, the lungs, even the brain, though those are rare. This tissue behaves like endometrial tissue: it responds to your hormonal cycle, it bleeds. But unlike the lining of your uterus, that blood has nowhere to go. It causes inflammation, scarring, adhesions. Over time, those adhesions can fuse organs together. Adenomyosis is different in a specific, important way. The tissue isn't outside the uterus — it's inside the wall of the uterus itself. Endometrial-like tissue invades the myometrium, which is the muscular layer. This makes the uterus larger, often boggy, and it changes how the uterine muscle contracts. The uterus is essentially fighting itself. Same family of cells. Completely different location. That distinction matters for everything that follows.

How the symptoms overlap — and where they split

This is where it gets genuinely complicated, because there's major overlap. Both conditions can cause: - Painful, heavy periods

• Pelvic pain that isn't just during your period
• Pain during sex
• Fatigue that doesn't make sense given how much you slept
• Fertility problems But there are some patterns that tend to lean one way or the other. Endo is more commonly associated with: - Pain that radiates — to the legs, the lower back, the rectum
• Pain during bowel movements or urination, especially around your period
• Pain that correlates with where the lesions are (bowel endo feels different from ovarian endo)
• Ovarian cysts (endometriomas — the "chocolate cysts" you may have heard of) A 2025 study ³ looked at over 3,000 patients who'd had surgery for endo and grouped them by phenotype — superficial endo, deep infiltrating endo (DIE), and adeno. The researchers found that different endo phenotypes were associated with distinct pain profiles, which confirms something a lot of us have suspected: "endo pain" isn't one thing. Where it is changes what it feels like. Adeno is more commonly associated with: - Extremely heavy periods — the kind where you're bleeding through products faster than seems possible
• A uterus that feels swollen or tender if a gyn presses on it
• Cramping that starts before your period and stays after
• A particular kind of deep pelvic pressure or heaviness
• Worsening symptoms over time, often as you get older One 2021 study ⁵ found something genuinely interesting here: adeno that affects the inner part of the uterine wall versus the outer part is associated with different clinical profiles. Inner myometrium adeno was more strongly linked to heavy menstrual bleeding and fertility issues; outer myometrium adeno had a stronger association with pain. So even within adeno, it's not one-size-fits-all.

The overlap problem: having both at once

This is probably the most important thing to know if you're newly diagnosed: these conditions frequently co-exist. Research consistently shows that a major proportion of people with endo also have adeno. Estimates vary — partly because adeno has historically been diagnosed at hysterectomy, which means it was missed in younger people who kept their uterus — but it's not rare. It's actually common enough that some researchers think they may share pathogenic mechanisms, even though they present differently. What this means practically: if you've been diagnosed with one, it's worth asking your gyn whether the other has been assessed. Not because it changes everything, but because it might change the treatment approach.

Why diagnosis is so different for each

This is one of the starkest differences between the two conditions, and it's one that causes a lot of pain in a non-physical sense. Endo can only be definitively diagnosed through surgery — specifically a laparoscopy (lap). This is one of the most frustrating things about the condition. Imaging can suggest it, especially for larger lesions or endometriomas, but you cannot rule out endo with an MRI or ultrasound. The average diagnostic delay is somewhere between 7 and 10 years depending on which study you read. If your lap came back "clear" but you have every symptom, it's worth knowing that: a general gynaecologist may miss lesions that a specialist in endo would find. Adeno can be diagnosed non-invasively — through MRI or transvaginal ultrasound (TVUS), by someone who knows what they're looking for. This is a real difference. It doesn't mean adeno is "easier" — it means the diagnostic path is different. Ultrasound features like myometrial cysts, asymmetrical thickening, or a heterogeneous myometrium can strongly suggest adeno. MRI can be even more specific. That said, imaging for adeno isn't perfect either, and there's a skill level involved in reading it. If your gyn is doing a quick scan and not specifically looking for adeno features, it can be missed.

The uterine contractility piece

One mechanism that's increasingly discussed in both conditions is uterine contractility — how the uterus contracts across the menstrual cycle. This isn't the same as labour contractions; it's a subtler, ongoing peristaltic movement that the uterus does all the time. There's growing evidence that this contractility is disrupted in both endo and adeno — and that this disruption may actually contribute to both symptoms and potentially to how the conditions develop in the first place ¹. The research here is still developing, and as one 2024 systematic review noted,

However, uterine peristalsis remains understudied, inconsistently measured, and poorly understood.

Salmeri N, Di Stefano G, Viganò P, et al. — Functional determinants of uterine contractility in endometriosis and adenomyosis: a systematic review and meta-analysis. Fertility and sterility, 2024. View paper →

. So it's real, it's relevant, and we don't have the full picture yet.

Treatment: where the paths converge and diverge

Both conditions are often managed hormonally first — the pill, the hormonal IUS (Mirena), GnRH agonists or antagonists, progestogens. The logic is similar: reduce or suppress the hormonal cycling that drives both conditions. But the surgical options differ. For endo, surgery involves excising or ablating the lesions. This is ideally done by a specialist — excision (cutting out the lesion) is generally considered more thorough than ablation (burning the surface). The skill of the surgeon matters enormously here. For adeno, surgery is more complicated because the tissue is inside the uterine wall. You can't just cut it out the same way. Options include adenomyomectomy (removing localised adenomyosis tissue), uterine artery embolisation, and — the treatment — hysterectomy. That last word is a lot to sit with, especially if you're under 40, or if you haven't had children, or if you just weren't ready to hear it. The decision about hysterectomy for adeno is not straightforward and deserves a whole conversation, not a paragraph. What's important to know: a hysterectomy does not treat endo. If you have both conditions and you have a hysterectomy for adeno, endo lesions elsewhere in the body remain. This is a important distinction that sometimes gets missed.

What the research actually says

The research on endo and adeno is growing, but it's also genuinely uneven. We know more about endo than adeno — partly because adeno was historically a condition diagnosed in older people after hysterectomy, which meant younger patients were invisible to the data. A few things the research does show clearly: The 2025 phenotype study ³ of over 3,000 surgical patients found that endo doesn't present the same way across phenotypes.

With regard to the established endometriosis classifications, it is hardly possible to draw conclusions from the endometriosis to the symptoms caused by it.

Hofbeck L, Au K, Blum S, et al. — Clinical characterization of endometriosis phenotypes. Archives of gynecology and obstetrics, 2025. View paper →

This matters because it pushes back on the idea that there's a "typical" endo presentation. There isn't. Which is part of why diagnosis takes so long. The 2021 study on adeno ⁵ broke down adenomyosis by location within the uterine wall — inner versus outer myometrium — and found these are associated with different clinical profiles. This is genuinely useful, because it suggests adeno isn't one monolithic condition either. Where in the uterine wall the tissue is matters for what symptoms you get. On the uterine contractility front, a 2024 systematic review and meta-analysis ¹ pulled together evidence from imaging, electrophysiology, and direct intrauterine pressure recording. The finding that

Evidence suggests that aberrant uterine contractility in nonpregnant women with endometriosis and adenomyosis contributes to symptoms and potentially heralds their pathogenesis.

Salmeri N, Di Stefano G, Viganò P, et al. — Functional determinants of uterine contractility in endometriosis and adenomyosis: a systematic review and meta-analysis. Fertility and sterility, 2024. View paper →

is major — it suggests the uterus's own movement patterns are part of the story, not just a consequence of it. On treatment, a 2024 randomised controlled trial ² looked at a specific hormonal combination (estetrol/drospirenone) in a cohort of 162 Japanese women with endo, using a placebo-controlled design. This is the kind of rigorous trial that's still relatively rare in endo research. Results showed efficacy for endo-associated pain, though it's worth noting this was a specific cohort and drug combinations affect people differently. What the research doesn't yet tell us clearly: why some people get endo, some get adeno, and some get both. The pathogenic mechanisms are still being worked out. There are theories — retrograde menstruation, stem cell involvement, immune dysfunction, lymphatic spread — but no single agreed explanation. The menstrual products study ⁴ examined whether products like tampons or cups play any role in pathogenesis; the honest answer from the current evidence is that we don't know, and the researchers were appropriately cautious about drawing conclusions. The honest summary: the science is moving, it's more than it used to be, and there's still a lot we don't know.

What to do with this

Here's what all of this actually means if you're living it. If you've been diagnosed with endo but your main symptoms are extremely heavy bleeding and a feeling of uterine heaviness or pressure — it's worth asking your gyn specifically whether adeno has been assessed. Not assumed, assessed. With imaging, by someone familiar with the signs. These are different conditions and they can co-exist. If you've been diagnosed with adeno but you also have pain that radiates, pain with bowel movements, or pain that doesn't seem to match a uterine source — same question in reverse. Ask whether endo has been formally ruled out, and what that ruling-out looked like. A transvaginal ultrasound that found adeno doesn't rule out endo elsewhere. If you're pre-diagnosis and trying to describe your symptoms to a gyn — try to be specific about the type of pain, not just the severity. Where is it? Does it radiate? Is it worse with bowel movements? Does it start before your period? Is the bleeding the main problem, or the pain, or both equally? These details help distinguish between conditions — and between phenotypes within endo — in ways that "really bad periods" doesn't. On treatment conversations: if someone is suggesting a hysterectomy for adeno and you also have or suspect endo, ask directly: what happens to the endo after the hysterectomy? The answer should involve a plan for that too, not just the adeno. On the emotional weight of a dual diagnosis: it is genuinely a lot. Two conditions, potentially two different treatment approaches, a body that is managing multiple things at once. That's not dramatic — that's just true. Give yourself time to process the information before you make decisions, if you can.