Dienogest, a selective progestin, reduces plasma estradiol level through induction of apoptosis of granulosa cells in the ovarian dominant follicle without follicle-stimulating hormone suppression in monkeys

Spontaneous recurrent menstrual pneumothorax: a case report

Introduction and importance

Endometriosis is most commonly found in the pelvic area, ~12% of people have it in other areas or organs, which is known as extrapelvic endometriosis. Thoracic endometriosis, which is also classified as extrapelvic endometriosis, manifests with four distinct forms: catamenial pneumothorax, catamenial hemothorax, catamenial hemoptysis, or lung nodules. Catamenial pneumothorax is the most common clinical symptom of these; however, it is frequently neglected by clinicians and goes undiagnosed and untreated. As a result, it is critical to raise awareness of this medical condition among clinicians.

Case presentation

The authors present a case report of a 34-year-old woman of reproductive age who had recurrent episodes of spontaneous pneumothorax during menstruation and underwent treatment with thoracoscopic surgery as well as gynaecological hormonal drugs including oral progesterone and dienogest throughout this time. Based on her symptoms, a catamenial pneumothorax caused by thoracic endometriosis was suspected.

Clinical discussion

The clinical symptoms, pathogenesis, diagnosis, and treatment of Catamenial Pneumothorax are analyzed. Furthermore, the usage of gynaecological hormone medications in this condition has been discussed. The mechanisms of oral contraceptives and progestin-based medications are evaluated by comparing the patient's treatment process, highlighting their pros and cons.

Conclusions

Thoracoscopic surgery combined with postoperative gynaecological hormonal medications may be the most effective treatment for this issue. Several gynaecological hormonal medicines are available, each of which has its own set of pros and cons, and must be thoroughly evaluated as well as correctly tailored to the patient's specific circumstances to have a positive therapeutic outcome.

Exploring the Impact of Endometrioma Aspiration and Dienogest Combination Therapy on Cyst Size, Inflammatory Cytokines in Follicular Fluid and Fertility Outcomes

Endometriomas (chocolate cysts) are cystic lesions that can develop on ovaries, and are characterized by the presence of ectopic endometrial tissue or similar tissue. Such lesions can cause a decline in the number and quality of oocytes, and lead to implantation failure. In this study, we retrospectively assessed the efficacy of repeated endometrioma aspiration and dienogest combination therapy in patients suffering endometriosis-associated infertility with endometriomas. A comparison was made between a treated group that underwent combination therapy followed by controlled ovarian hyperstimulation (COH) (n = 30) and a control group that did not undergo treatment (n = 40), at the IVF Osaka Clinic from September 2019 to September 2021. There were no differences in patient background between the two groups. A reduction in endometrioma size continued for 12 months after treatment. The numbers of follicles that developed to 15 mm or greater in size following COH and mature oocytes were significantly lower in the treated group compared to those in the control group. The levels of inflammatory cytokines in the follicular fluid significantly decreased in the treated group (p < 0.05). In patients in the treated group who underwent a second ova retrieval, the results were compared between those in the first ova retrieval (immediately after the end of treatment) and those in the second ova retrieval (four months after the first retrieval). The numbers of follicles following COH, retrieved, mature and fertilized ova were significantly increased in the second ova retrieval.

Impact of dienogest pretreatment on IVF-ET outcomes in patients with endometriosis: a systematic review and meta-analysis

BACKGROUND

To comprehensively evaluate the influence of dienogest (DNG) versus non-DNG pretreatment on in vitro fertilization and embryo transfer (IVF-ET) outcomes for patients with endometriosis.

METHODS

PubMed, Embase, Cochrane Library, Web of Science, CNKI, WanFang, and VIP were comprehensively searched for relevant publications until September 14, 2022. Primary outcomes included clinical pregnancy rate and live birth rate. Secondary outcomes included retrieved oocytes, mature oocytes, blastocysts, growing follicles, transferrable embryos, fertilization rate, implantation rate, and miscarriage rate. Subgroup analysis was performed according to different grouping methods and embryo types.

RESULTS

Five studies of 568 females with endometriosis were involved in this systematic review and meta-analysis. DNG treatment exhibited similar effects to non-DNG treatment on either the primary or the secondary outcomes (all P > 0.05). The DNG group had a significantly greater clinical pregnancy rate than the non-hormonal treatment group (pooled relative risk [RR]: 2.055, 95% confidence interval [CI]: 1.275, 3.312, P = 0.003), and exhibited a significantly lower clinical pregnancy rate than the long gonadotropin-releasing hormone agonist (GnRH-a) group (RR: 0.542, 95%CI: 0.321, 0.916, P = 0.022). For patients undergoing fresh embryo transfer, the DNG group displayed a significantly greater clinical pregnancy rate versus the non-DNG group (pooled RR: 1.848, 95%CI: 1.234, 2.767, P = 0.003). Patients receiving DNG had a significantly greater live birth rate than those with non-hormonal treatment (pooled RR: 2.136, 95%CI: 1.223, 3.734, P = 0.008), while having a significantly lower live birth rate than the long GnRH-a group (RR: 0.441, 95%CI: 0.214, 0.907, P = 0.026). While using fresh embryos, patients with DNG treatment had an increased live birth rate, compared with those without DNG treatment (pooled RR: 2.132, 95%CI: 1.090, 4.169, P = 0.027).

CONCLUSION

DNG treatment may have similar effects to non-DNG treatment on IVF-ET outcomes. The clinical pregnancy rate and live birth rate after DNG treatment may be significantly higher than those after non-hormonal treatment. More evidence is warranted to corroborate these findings.

Low-density small extracellular vesicles in bovine follicular fluid carrying let-7i target FASLG to inhibit granulosa cells apoptosis

Apoptosis of granulosa cells is a key factor in mammalian follicular atresia. It has a significant impact on oocyte development and maturation. Extracellular vesicles (EVs) are a group of highly heterogeneous population. Previous studies have found that ovarian follicular fluid is rich in EVs. In the present study, the follicular fluid of 3-5 mm follicles from bovine ovaries without corpus luteum was collected, and a subtype of small EVs (sEVs), low-density small EVs (LD-sEVs), was successfully isolated by differential ultracentrifugation combined with iodixanol density gradient centrifugation. LD-sEVs were identified using transmission electron microscope, nanoparticle tracking analysis and Western blot. Flow cytometry, Quantitative reverse transcription PCR (RT-qPCR), Western blot, and other methods were used to detect the effect of LD-sEVs on follicular granulosa cell apoptosis. After that, let-7i, a highly expressed miRNA component in LD-sEVs, was screened and target validation was carried out in granulosa cells. The results showed that LD-sEVs could be taken up by granulosa cells and inhibited the apoptosis. Further research found that let-7i inhibits the apoptosis of granulosa cells by targeting FASLG. It plays an important role in regulating the apoptosis of follicular granulosa cells, which may affect follicular development.

Prediction of the final menstrual period in women taking Dienogest using estradiol and follicle-stimulating hormone values: a case-control study

Dienogest (DNG) is widely used to treat dysmenorrhea associated with estrogen-dependent diseases such as endometriosis and adenomyosis. DNG becomes unnecessary after menopause when estrogen secretion declines drastically. However, there are no clear criteria for when to halt DNG in perimenopausal patients. Menstruation and dysmenorrhea often resume after discontinuation due to approaching menopause. This case-control study used serum estradiol and follicle-stimulating hormone (FSH) levels to predict whether menstruation would resume in perimenopausal women after discontinuation of DNG. The study enrolled patients aged ≥40 years with endometriosis and/or adenomyosis and who had either completed oral DNG therapy (DNG group) or had spontaneous menopause without hormone therapy (control group). We assessed estradiol and FSH values before DNG termination or the final menstrual period. DNG group members that resumed menstruation after DNG termination (D (+) group, n = 17) had significantly higher estradiol and lower FSH levels than those who did not (D (-) group, n = 22) up to four months before DNG termination but not from four to 12 months. Estradiol and FSH levels were not significantly different between the D (-) and control groups. Receiver operating characteristic curves created from the estradiol and FSH values indicated that menstruation resumed when levels were ≥17 pg/mL and <100 mIU/mL, respectively. In contrast, menstruation did not resume in cases of estradiol ≤20 pg/mL and FSH >80 mIU/mL. The study results provide useful criteria for deciding when to terminate DNG in perimenopausal patients that consider their tolerance for resuming menstruation. Applications to menopause-inducing therapy for uterine fibroids and other conditions are anticipated. Further large-scale studies are needed.

New treatment strategy for endometriosis using progestin-primed ovarian stimulation with dienogest: A prospective cohort study, comparison of dienogest versus dydrogesterone

Dienogest (DNG) is an oral progestin effective for the treatment of symptomatic endometriosis, such as reduction of endometrial lesion and control of pain intensity. Progestin-primed ovarian stimulation (PPOS) is a new controlled ovarian hyperstimulation (COH) regimen, and several reports have shown that dydrogesterone (DYG) is an appropriate progestin for PPOS. The purpose of this study was to evaluate the efficacy of DNG in patients undergoing PPOS during COH in comparison with DYG. This was a prospective, cohort, parallel-group, non-inferiority trial of 150 women with endometriosis undergoing assisted reproductive technology between February 2018 and May 2020 at the single fertility center. The assignment to each protocol was based on the optimal treatment for each patient. Patients taking DNG 2 mg continuously were assigned in the DNG group(n = 73). The other patients were allocated in DYG group(n = 77). All viable embryos were cryopreserved for subsequent transfer. The main outcome measures were the mature oocyte and fertilization rates. During this study, no premature LH surge was detected. A smaller number of oocytes were retrieved in the DNG group than in the DYG group (6.18 ± 3.60 vs. 9.85 ± 5.77); however, the rate of mature oocytes was significantly higher in the DNG group than in the DYG group (89.1 % vs. 78.9 %). The fertilization rate was comparable between two groups. Therefore, patients taking DNG for PPOS can continue endometriosis treatment and obtain good-quality embryos during COH. Further prospective randomized-controlled trial should be performed to confirm of this novel strategy of DNG.

The clinical outcome of Dienogest treatment followed by in vitro fertilization and embryo transfer in infertile women with endometriosis

BACKGROUND

Endometriosis is considered to be the most intractable cause of female infertility. Administering any type of treatment for endometriosis before in vitro fertilization and embryo transfer (IVF-ET) is an important strategy for improving the IVF-ET outcomes for infertile women with endometriosis. In fact, treatment with a gonadotropin-releasing hormone (GnRH) agonist just before IVF-ET has been reported to improve the clinical outcome in endometriosis patients. However, the benefit of Dienogest (DNG), a synthetic progestin, treatment just before IVF-ET remains unclear.

METHODS

Sixty-eight infertile women with Stage III or IV endometriosis (ovarian endometrial cyst < 4 cm) were recruited for this study. The subjects were divided into 2 groups: a DNG group (n = 33) and a control group (n = 35). DNG was administered orally every day for 12 weeks prior to the conventional IVF-ET cycle in the DNG group. Standard controlled ovarian hyperstimulation with the GnRH agonist long protocol was performed in the control group. The numbers of mature follicles and retrieved oocytes, fertilization rates, implantation rates, and clinical pregnancy rate were compared between the two groups. In addition, the concentrations of inflammatory cytokines, oxidative stress markers, and antioxidants in follicular fluids were also measured.

RESULTS

The numbers of growing follicles, retrieved oocytes, fertilized oocytes, and blastocysts were significantly lower in the DNG group than in the control group. The fertilization and blastocyst rates were also lower in the DNG group than in the control group. Although there was no significant difference in the implantation rate between the groups, the cumulative pregnancy rate and live birth rate were lower in the DNG group than in the control group. There was no significant difference in the abortion rate. Our results failed to show that DNG reduces the inflammatory cytokine levels and oxidative stress in follicular fluids.

CONCLUSIONS

Administering DNG treatment just before IVF-ET did not provide any benefits to improve the clinical outcomes for infertile women with endometriosis.

Dienogest suppresses the activation of primordial follicles and preserves the primordial follicle stockpile for fertility in mice

The aim of the present study was to characterize the effect of long-term usage of dienogest, a fourth-generation progestin that possesses progestogen and anti-androgen activities, on the stockpile of oocytes and fertility after administration. Female ICR mice (100 days old) were divided into a dienogest group and a control group. The mice received 16 consecutive subcutaneous injections of 5 mg dienogest dissolved in corn oil or corn oil as a vehicle control every 4 days. The mice treated with dienogest had more total offspring and larger litter sizes after the final administration than the mice treated with the vehicle control. Greater numbers of primordial follicles were detected at both 4 and 80 days after the final administration. No significant differences were found in serum anti-Müllerian hormone concentrations at 4 and 80 days after the final dienogest administration. The ratio of primary to primordial follicles was decreased in 3-day-old newborn ovaries cultured for 4 days with dienogest (10^-7, 10^-6 and 10^-5 mol/l) compared with ovaries cultured without dienogest. The results of the present study indicate that dienogest suppresses the activation of primordial follicles during its administration and preserves the primordial follicle stockpile and subsequent fertility in mice.

Progestins for the Treatment of Endometriosis: An Update

Endometriosis is a gynecological condition that affects approximately 10% of women of reproductive age, including 25–40% of infertile women. Dysmenorrhea, dyspareunia and chronic pelvic pain are the most common symptoms. Currently available medical therapies for endometriosis do not cure the disease, but are directed at symptom relief, typically utilizing the hormone responsiveness of endometriotic tissue to induce lesion atrophy. Unfortunately, pain relapse after treatment suspension is a common event. Treatment with pharmacological therapies for endometriosis should be conceived in terms of years, thus agents that must be withdrawn after a few months due to poor tolerability or severe metabolic side effects do not greatly benefit women with symptomatic endometriosis. The characteristics of progestins render this class an ideal pharmacological choice for administration over extended periods. The present paper will review the rationale for using progestins and their mechanism of action in endometriosis. Thereafter, the results obtained by various progestins in the treatment of endometriosis will be evaluated (danazol, gestrinone, norethisterone acetate, desogestrel, cyproterone acetate, megestrol acetate, medroxyprogesterone acetate, and levonorgestrel). A progestin called dienogest, recently introduced for the treatment of endometriosis, will be given special focus, describing its mechanism of action and clinical results.

Primary umbilical endometriosis successfully treated with dienogest

Primary umbilical endometriosis (PUE) is a rare gynaecological disorder. A majority of the reported cases were treated with surgical excision as medical treatment had been found to be less successful. We reported a case of PUE successfully treated with dienogest without any profound side effects from the drug.

Innovative approach in assessing the role of neurogenesis, angiogenesis, and lymphangiogenesis in the pathogenesis of external genital endometriosis

Endometriosis is a chronic, progressive, relapsing estrogen-dependent disorder characterized by the growth of tissue structure and function similar to the endometrium outside the normal mucosa of the uterine cavity localization. Endometriosis is found in 10-15% of women in reproductive age and it is one of the main causes of pelvic pain syndrome and infertility. Mechanisms of the development of endometriosis and related pathological pain impulses are still poorly understood and therapeutic approaches do not always have a sufficient effect; in this connection, the study of the pathogenesis of endometriosis and endometriosis-associated pain currently is perspective. Identification of significant factors of angiogenesis, lymphangiogenesis, and neurogenesis in the external genital endometriosis will promote the development of non-invasive early diagnosis and pathogenetic therapy.

Outcomes of treatment with cyclic administration of dienogest after ovarian endometriotic cystectomy

To evaluate the outcomes of patients treated with cyclic administration of dienogest after ovarian endometriotic cystectomy, following the completion of treatment. We retrospectively evaluated 26 patients treated with dienogest (2 mg/day) after cystectomy (revised American Society for Reproductive Medicine [r-ASRM] stage III-IV) in a pilot study. Dienogest was administered cyclically, for a total of six cycles, each comprising three weeks on and one week off. Outcomes of interest included severity of menstrual pain and recurrence of cysts at baseline, during the immediate post-treatment period and at the final outpatient follow-up. The mean outpatient follow-up period was 45.0 months. The visual analog scale score for menstrual pain following 6 cycles of dienogest treatment was significantly lower than that at baseline; it remained low at the final follow-up. The recurrence rates of cysts were 4% and 21% at 24 and 48 months after the completion of dienogest treatment, respectively. Six patients with recurrent disease were all classified as having r-ASRM stage IV. Our results suggest that cyclic dienogest for six months after cystectomy could relieve menstrual pain and reduce the recurrence of cysts, for approximately four years. The necessary treatment period for patients with r-ASRM stage IV disease requires further study.

Protective effect of dienogest on chemotherapy-induced reduced fertility in female rats

Reduced fertility is one of the main long-term consequences of chemotherapy given for lymphoma, leukemia, and other malignancies in young women. We examined with a female rat model whether and how dienogest, a fourth-generation progestin, modulates reduced fertility following exposure to gonadotoxic chemotherapy. Female rats were administered cyclophosphamide with or without GnRH agonist and different concentrations of dienogest for 20 days. Animals were sacrificed on Day 29, and the numbers of follicle at primordial, preantral and antral stage in the ovaries were counted histologically. Rats treated with sterile saline solution (as control), cyclophosphamide, cyclophosphamide plus GnRH agonist, and cyclophosphamide plus dienogest were also mated with male rats to evaluate their fertility and pregnancy outcomes. Cyclophosphamide significantly reduced the number of primordial follicles, whereas dienogest suppressed depletion of primordial follicle pool induced by chemotherapy. Although the rats exposed to cyclophosphamide alone failed to deliver live births, co-treatment with dienogest improved the pregnancy outcomes of treated rats. The protective effect of dienogest on chemotherapy-induced ovarian damage and reduced fertility was comparable to that of GnRH agonist. The present results suggest that the co-administration of dienogest and chemotherapy may be a useful strategy in preserving ovarian function and fertility in premenopausal women facing gonadotoxic chemotherapy.

Relief of uterine bleeding by cyclic administration of dienogest for endometriosis

OBJECTIVE

This study assessed the relief of uterine bleeding and clinical symptoms during cyclic administration of dienogest for the treatment of endometriosis.

METHODS

In total, 25 patients undergoing ovarian cyst enucleation and given dienogest participated in this study. Dienogest 2 mg/day was administered for 3 weeks, and the drug was then withdrawn for 1 week (cyclic administration of dienogest). This 4-week cycle was repeated six times. Patients' records were prospectively analyzed for the number of days on which any uterine bleeding occurred, as well as menstrual pain before and after the start of dienogest administration were evaluated with a view to using the data obtained herein as the basis.

RESULTS

During the period of cyclic administration of dienogest, uterine bleeding occurred on 5.8 to 7.7 days per 4-week period on an average through cycles. Of uterine bleeding episodes, menstruation-like uterine bleeding was present in about 80% of patients. The visual analog scale (VAS) value for menstrual pain significantly decreased from 3.8 before dienogest administration after surgery to 1.5 at the completion of cycle 1, VAS remained low thereafter.

CONCLUSION

These results raise the possibility that cyclic administration of dienogest may relieve lessen uterine bleeding, a major adverse event and menstrual pain.

Dienogest was effective in treating hemorrhagic ascites caused by endometriosis: a case report

Hemorrhagic ascites caused by endometriosis is extremely rare, and its treatment is under discussion. We report a case of recurrent endometriosis-related ascites treated with dienogest (DNG). A 35-year-old nulliparous Japanese woman with a history of infertility presented with worsening dysmenorrhea and abdominal distention caused by massive ascites. The patient underwent exploratory laparotomy, and hemorrhagic ascites (5500 mL) was drained. She had a normal-sized uterus, and the bilateral ovaries could not be observed because of extensive adhesion in the abdominal cavity. Endometriosis was diagnosed by histopathological evaluation of the omental biopsy, and this was considered to be the cause of ascites. After laparotomy, she had recurrence of ascites. For the next 8 years, the patient was treated conservatively with gonadotropin-releasing hormone agonist therapy and drainage during the intermittent periods followed by DNG administration. She has been treated continuously with DNG for 1 year with no recurrence of ascites. DNG could be an effective treatment for recurrent ascites associated with endometriosis, especially when surgical therapy is undesirable.

Effect of a dienogest for an experimental three-dimensional endometrial culture model for endometriosis

The pathogenesis of endometriosis remains poorly understood at least in part because early stages of the disease process are difficult to investigate. Previous studies have proposed a three-dimensional fibrin matrix culture model to study human endometriosis. We examined the ultrastructural features of the endometriosis in this model and assessed the effect of a progestin on endometrial outgrowth and apoptosis in this culture system. Endometrial explants were placed in three-dimensional fibrin matrix culture and treated with and without various concentrations of the progestin dienogest. By the second week, endometrial gland-like formation was established in outgrowths both attached to and at a distance from the explants. These cells formed a combination of clumps and tubular monolayers surrounding a central cavity. Electron microscopy demonstrated that these cells are polarized with microvilli on the apical surface, desmosome-like structures, and basement membrane; features consistent with glandular epithelial cells. Outgrowth of endometrial stromal cells and glandular formation was impaired in response to dienogest in a dose-dependent manner. Our study shows that the human endometrial explants cultured in three-dimensional fibrin matrix establish outgrowths that ultrastructurally resemble ectopic endometrial implants. This model may provide insight into the cellular processes leading to endometriosis formation and enables screening of therapeutic compounds.

Effectiveness of the cyclic administration of dienogest in a case of pathological disappearance of intestinal endometriosis

We have reported good control of atypical genital bleeding when using a cyclic administration of dienogest (repeated 4-week cycles, each consisting of the administration of 2 mg/day of dienogest for 3 weeks, followed by 1 week of drug withdrawal) in patients with endometriosis. Herein, we report the effectiveness of the long-term cyclic administration (22 months) of dienogest in a case of pathological disappearance of intestinal endometriosis diagnosed by endoscopy and histology of the lower gastrointestinal tract. There is no recurrent sign after 16 months of the treatment being stopped. Atypical genital bleeding during treatment was 3–5 days a month in each cycle. Compliance was good, so we could continue the therapy. The long-term cyclic administration of dienogest in patients with intestinal endometriosis may have significant merit.

Dienogest in long-term treatment of endometriosis

Endometriosis is a chronic disease primarily affecting women of childbearing age, in which endometriotic lesions form outside the uterus, typically leading to painful symptoms, fatigue, and infertility. The symptoms of endometriosis may cause significant impairment in quality of life and represent a substantial economic burden to patients, families, and society. There is no cure for endometriosis; management consists of alleviating pain and other symptoms, reducing endometriotic lesions, and improving quality of life. Recurrence after surgical intervention is common, while the clinical evidence to support the efficacy and safety of many medications currently used in endometriosis is limited. Dienogest is an oral progestin that has been investigated extensively in the treatment of endometriosis in two clinical programs performed in Europe and Japan, including dose-ranging, placebo-controlled, active comparator-controlled, and long-term (up to 65 weeks) studies. These studies demonstrated that dienogest 2 mg daily effectively alleviates the painful symptoms of endometriosis, reduces endometriotic lesions, and improves indices of quality of life. Dienogest showed a favorable safety and tolerability profile in these studies, with predictable adverse effects, high rates of patient compliance, and low withdrawal rates. This review article describes the clinical trial evidence that characterizes the efficacy and safety of dienogest in endometriosis, including two studies characterizing dienogest in long-term use. The relevance of these findings to the management of endometriosis in clinical practice is discussed.

Dienogest: a new therapeutic agent for the treatment of endometriosis

Dienogest (DNG), a progestin of 19-nortestosterone derivative, has good oral bioavailability and is highly selective for progesterone receptors. Owing to its antiovulatory, antiproliferative activities in endometrial cells, and its inhibitory effects on the secretion of cytokines, DNG is expected to be an effective treatment for endometriosis. Progesterone receptor-binding affinity is higher for DNG than for progesterone. Several pilot studies demonstrated that after 24 weeks of DNG treatment, there was a significant decrease in terms of dysmenorrhea, premenstrual pain, dyspareunia and diffuse pelvic pain. Most of the cases of genital bleeding occurring in the DNG treatment were spotting or breakthrough bleeding, which decreased with continued treatment and resolved either during treatment or after the end of treatment. The therapeutic effects of DNG 2 mg/day and norethisterone acetate 10 mg/day for endometriotic symptoms during a period of 24 weeks were almost similar. The only disadvantage of DNG seems to be the irregular bleeding. Good efficacy and tolerability of DNG in patients with endometriosis have been demonstrated in an open, randomized European clinical trial as compared with norethisterone acetate. In Japan, a Phase III, randomized, double-blind, multicenter, controlled trial was conducted to compare the efficacy and safety of DNG with intranasal buserelin acetate in patients with endometriosis. The study demonstrated that DNG is as effective as intranasal buserelin acetate in alleviating endometriosis symptoms, and causes less bone mineral density loss, resulting in the use on a commercial basis for endometriosis patients in Japan from 2008. This paper provides summarized data on this new promising drug for endometriosis.

Progestin effects in endometriosis treatment: new research on mechanisms

New research on mechanisms of progestin effects in endometriosis treatment has been performed with dienogest (DNG), which has recently been launched in this regard. It is effective in the same low dosage of 2 mg/day, similar to the use of contraception and hormone therapy, whereas other progestogens (with the exception of dydrogesterone) must be given in much higher dosages to treat typical symptoms of endometriosis. This short review summarizes experimental studies on DNG. They demonstrate strong antiproliferative effects in endometrial and endometriotic cells or experimental endometriosis, as well as anti-inflammatory and antiangiogenic actions. By direct action on the ovarian folliculogenesis DNG lead to only modest suppression of estradiol production in contrast to the high-dosed progestogens or to gonadotropin releasing hormone (GnRH) agonists. These effects add to the well-known tolerability because DNG is very neutral regarding cardiovascular, metabolic or central action which also makes it suitable for long-term therapy.