Happy Fact Friday! Each week we pick one piece of new endometriosis or adenomyosis research and break it down in plain language, so you can walk away with something useful to think about or bring up at your next appointment. This week’s pick is a real-world study on dienogest, one of the most commonly prescribed hormonal treatments for endometriosis, published in the Journal of Gynecology Obstetrics and Human Reproduction in September 2026. Rather than testing the drug in a tightly controlled clinical trial, the researchers went straight to the people actually taking it and asked: does this help, and what does it cost you to take it?

If you’ve been diagnosed with endometriosis (a condition where tissue similar to the lining of the uterus grows outside the uterus, causing pain, inflammation and sometimes fertility difficulties), there’s a good chance dienogest has come up in conversation with your doctor. Dienogest is a type of progestin, a synthetic form of the hormone progesterone. It works by suppressing estrogen’s effects on endometrial-like tissue, which can shrink or quiet down the lesions that cause pain, and it also thins the lining of the uterus, which often reduces how heavy and painful periods are.

It’s been used across Europe and elsewhere for over a decade as a first- or second-line medical therapy for endometriosis, usually taken as a daily tablet. Clinical trials run by pharmaceutical manufacturers have shown it can meaningfully reduce pelvic pain. But clinical trials are conducted under fairly controlled conditions, with selected participants, close monitoring, and a defined follow-up period. What clinical trials don’t always capture well is what happens when the medication is prescribed in everyday, real-world practice: to people juggling work, family, other health conditions, and their own tolerance for side effects, over however long they personally choose to stay on it. That’s the gap this new study tried to fill.

A team of French researchers, led by Pauline Prost and colleagues at Nimes University Hospital, ran what’s called a cross-sectional, patient-reported study. In plain terms, that means they didn’t follow patients forward in time from the day they started treatment; instead, they surveyed people who were already being cared for within a regional endometriosis care network between April 2024 and September 2025, and asked them to look back and report on their own experience with dienogest, how their symptoms and quality of life compared before starting the medication versus while taking it, along with any side effects they noticed and whether they stayed on the drug or stopped.

In total, 146 patients with endometriosis completed the questionnaire. Of those, 123 had reported painful periods (called dysmenorrhea) before starting dienogest, which gave the researchers a solid group to measure pain improvement against. Because this was based on people’s own memories and self-ratings rather than clinical measurements taken in real time, it’s sometimes called “real-world evidence,” useful precisely because it reflects lived experience, but with its own limitations, which we’ll come back to.

Nearly half of patients who had painful periods before starting dienogest, 44.7% (55 out of 123), reported that their dysmenorrhea completely resolved once they were on treatment. That’s not “a bit better,” that’s gone entirely, for a large share of respondents. It’s worth reading that figure alongside what’s in the next section rather than on its own: a substantial number of patients who experienced this kind of relief still ended up stopping the drug because of how it made them feel day to day. That tension, real symptom relief and real tolerability problems sitting side by side in the same group of patients, is what this kind of study is actually useful for showing, more than either number is on its own.

Overall quality of life also improved in a way that was statistically significant, meaning it’s very unlikely to be down to chance. Patients rated their quality of life, on average, at 4.4 before starting dienogest, rising to 5.5 while on treatment. One caveat worth flagging: the study reports this as a self-rated global quality-of-life score but doesn’t specify what scale patients were rating against, so it isn’t clear whether 5.5 represents a modest step up on a 0-to-10 scale or a bigger relative jump on a narrower one. That doesn’t undermine the statistical significance of the improvement, but it does mean the numbers are harder to size up at a glance than they first appear.

It’s worth pausing on why any of this matters beyond the numbers. Endometriosis is notorious for the length of time it takes to get diagnosed and for how often patients are told their pain is “normal” or “just bad periods.” A study built from what patients themselves reported pushes back on that dismissiveness, and it puts real weight behind the idea that meaningful symptom relief is achievable for a substantial number of people with the right treatment. It just doesn’t come free for everyone, which is exactly what the next section is about.

Every single patient in the study, 100%, reported experiencing at least one side effect while taking dienogest. On its own that number sounds dramatic, but it’s worth some context: this was a checklist-style question, and self-report checklists covering common, low-specificity symptoms like fatigue or low mood tend to land close to 100% for “at least one” in almost any real-world drug survey, simply because most people will tick at least one box. The more informative numbers are the specific rates:

• Fatigue, reported by 63.0% of patients
• Decreased libido (reduced sex drive), reported by 58.3% of patients
• Mood disturbances, reported by 50.7% of patients

These weren’t rare or minor complaints, they were the norm in this group, and the impact was substantial: 40.4% of patients discontinued dienogest altogether, with the researchers noting that adverse effects were the main driver of stopping treatment. In other words, even though the medication clearly helped pain and quality of life for many people while they were taking it, a large minority found the trade-offs weren’t sustainable long-term.

The study also noted that how symptoms improved and which side effects showed up seemed to vary depending on how long someone had been on the medication, hinting that the experience of taking dienogest may shift over time rather than staying constant from day one.

If you’re currently taking dienogest, have taken it in the past, or are weighing it as an option with your doctor, this research offers a genuinely balanced, patient-grounded picture rather than a marketing pitch or a worst-case horror story. A few practical takeaways stand out.

Real, meaningful relief is possible for a substantial share of people, but it comes with a real chance of side effects that are common enough to plan for, not exceptions to expect to avoid. If you’re on dienogest and struggling with whether it’s “supposed to” feel this different, either in symptom relief or in side effects, this data suggests both are realistic and common outcomes, not a fluke or a sign something has gone wrong.

If you’re dealing with fatigue, changes in libido, or mood shifts while on dienogest, you’re describing exactly what the majority of patients in this study also went through. That doesn’t mean you have to simply tolerate it, it means these are known, well-documented effects worth actively discussing with your healthcare provider, who may be able to help you manage them, adjust your dose or timing, or discuss whether an alternative treatment might suit you better.

It’s reasonable to reassess over time. With four in ten patients stopping the medication, largely due to side effects, this study is a useful reminder that treatment plans for endometriosis often aren’t “set and forget.” What works, or doesn’t, for you in month one may look different by month twelve, and revisiting the conversation with your care team periodically is a completely normal part of managing a chronic condition like endometriosis.

Your experience is data, too. This entire study exists because researchers valued what patients themselves reported about their own bodies and lives. If your clinician isn’t asking how a treatment is actually affecting your day-to-day quality of life, not just your pain score, this research is a good prompt to bring that conversation up yourself.

No single study, however useful, tells the whole story, and this one has some real limitations worth keeping in mind. It was a cross-sectional design, meaning patients were surveyed at one point in time and asked to recall how things were before treatment; memory isn’t perfect, and this kind of retrospective self-report can be shaped by how someone feels right now, known as recall bias. There was also no comparison or control group of similar patients who didn’t take dienogest, so we can’t be completely certain how much of the reported improvement is specifically attributable to the drug versus other factors, such as the natural fluctuation of symptoms over time or the effect of simply receiving more attentive care.

The sampling frame is also worth thinking about carefully. Everyone surveyed was still engaged with the regional care network at the time of the questionnaire. Patients who had a bad enough experience with dienogest that they disengaged from care entirely, switched clinics, or were lost to follow-up are likely underrepresented here. That would tend to bias the sample toward more tolerable, more successful outcomes, which means the real-world discontinuation rate could plausibly be higher than 40.4%, not lower, once people outside this care network are accounted for.

The sample, 146 patients drawn from one regional care network in France, is also relatively modest and geographically limited, so results may not translate identically to every population, healthcare system, or individual. The published abstract also doesn’t state a funding source or conflict-of-interest disclosure for the study, so readers weighing how independent this evidence is don’t have that information from what’s publicly available. Finally, because participation depended on patients being willing and able to complete a questionnaire, the group surveyed may not perfectly represent everyone who has ever taken dienogest.

• In this real-world study of 146 endometriosis patients, dienogest completely resolved painful periods for 44.7% of those who had them, and overall quality of life improved significantly, though the study doesn’t specify the scale that quality-of-life score was measured on.
• Every patient in the study reported at least one side effect, most commonly fatigue (63.0%), decreased libido (58.3%), and mood disturbances (50.7%); the near-universal “any side effect” figure is partly a feature of how the question was asked, so the specific rates matter more than the headline 100%.
• 40.4% of patients discontinued dienogest, mainly because of these side effects, and because everyone surveyed was still in contact with their care network, the true discontinuation rate in the wider population could be even higher.
• This was a retrospective, patient-reported study without a control group or disclosed funding information, so it should be read as a real-world snapshot rather than definitive proof of cause and effect.
• If you’re on dienogest, or considering it, the balance of relief versus side effects is worth an open, ongoing conversation with your healthcare provider.

This “Fact Friday” is based on one study, and while it adds valuable real-world insight to what we know about dienogest, it isn’t a substitute for personalised medical advice. Endometriosis and adenomyosis affect everyone differently, and decisions about hormonal treatment should always be made together with your own gynaecologist or healthcare provider, who knows your full history, your goals (including whether fertility is a current consideration), and what other options might be available to you.

Thanks for reading this week’s Fact Friday. If a friend or family member is navigating an endometriosis or adenomyosis diagnosis, feel free to pass this along, understanding what real patients experience with common treatments can make those first conversations with a doctor feel a little less daunting.