Design: This study is a retrospective analysis of patients who were prescribed norethindrone for endometriosis. We examined associations between pain improvement and sociodemographic and clinical characteristics, including patient age, race, phenotype of endometriosis, treatment duration, body mass index (BMI), and surgical history. Chi-square and Fisher’s exact tests were used to assess statistically significant differences between patient characteristics and pain improvement. Log binomial regression was used to estimate risk ratios (RR) and 95% confidence intervals (CI) representing the association between patient characteristics and pain improvement.

Setting: Academic referral center for endometriosis.

Patients or Participants: This study was conducted on all patients who presented to our center from 2016-2022 and were prescribed norethindrone. Patients who had missing pain and length of treatment data, a treatment duration of <4 months, and/or other concurrent medical treatments were excluded. A total of 145 patients were included in the final analysis.

Interventions: N/A

Measurements and Main Results: 120 patients (84%) reported improvement of pain with norethindrone. Patient age, race, and BMI were not associated with significant decrease in treatment response. A length of treatment of ≤ 6 months was significantly associated with no pain improvement (RR:5.40, 95%CI:1.62-18.00). Phenotype of endometriosis, and concomitant fibroids or adenomyosis were not associated with a significant difference in treatment response. Patients with a history of excision of endometriosis were also at a higher risk of no pain improvement, though not statistically significant (RR:3.00, 95%CI:0.74-12.19).

Conclusion: Norethindrone was associated with pain improvement in most patients in this study. Norethindrone may be an effective treatment for endometriosis patients with different phenotypes, as well as those with concomitant fibroids and adenomyosis. This study elucidates patient characteristics that may be associated with pain improvement with norethindrone; this can aid clinicians in formulating treatment plans for patients with endometriosis.