The LUNA study is a prospective, randomized, double-blind, sham-controlled, decentralized clinical trial in participants with heavy menstrual bleeding of no known structural cause. The study includes two age-based cohorts: adolescents aged 14-21 and adults aged 22-45. Participants in both cohorts will be randomized to receive transcutaneous auricular neurostimulation (tAN), which targets the auricular branch of the vagus nerve (ABVN) and the auriculotemporal nerve (ATN), or sham stimulation. Participants will be enrolled into the study over the course of five consecutive menstrual cycles. All study activities will occur remotely and in addition to participants' typical treatment for HMB (as allowed by the eligibility criteria).

During the first two consecutive menstrual cycles (M1 - M2, "Baseline Phase"), no tAN treatment will be delivered. Participants will estimate blood loss using the Pictorial Bleeding Assessment Chart (PBAC), and menstrual cramp pain will be assessed with a Numerical Rating Scale (NRS), daily throughout the duration of the menstruation phase of their two baseline menstrual cycles. Menstrual symptoms will be assessed using the Cox Menstrual Symptom Scale (CMSS) and a general quality of life assessment will be conducted on the final day of menstruation using the RAND Short-Form 36 (RAND-36). Menstrual-related quality of life assessments will also be conducted on the final day of each menstruation using the Menstrual Bleeding Questionnaire (MBQ) in the adult cohort, and the adolescent version (aMBQ) in the adolescent cohort.

During the following three consecutive menstruations (M3 - M5, "Treatment Phase"), participants will self-administer one 2-hour sham or active tAN session daily, beginning Day 1 of menstruation through the final day of menstruation in each menstrual cycle. Blood loss (via the PBAC) and menstrual cramp pain (via the NRS) will be assessed daily throughout the duration of each menstruation. Quality of life will be assessed with the CMSS, RAND-36, and the MBQ (adults) or aMBQ (adolescents) on the final day of each menstruation. A device usability survey will be completed at the end of M3 and M5. Participants will exit the study after the final day of M5.

Inclusion Criteria:

1. Regularly menstruating female aged 14-45 years at time of screening
2. History of menorrhagia as assessed by the Menorrhagia Screening Tool
3. Stable/consistent use of current non-hormonal medications and supplements for the past three months, willingness to continue use for duration of study, and not start any new medications or homeopathic remedies
4. Reliable access to an internet-enabled device to complete required questionnaires that is compatible with the study application (iOS 18 and Android 15 or greater)
5. Willingness to consistently use only study-provided menstrual products throughout duration of the study
6. Participant PBAC scores are ≥150 for both baseline menstruation months

Exclusion Criteria:

1. Pregnancy within three months of enrollment
2. Lactating at the time of enrollment
3. Typical length of menstruation greater than 14 days
4. Antifibrinolytic (i.e. tranexamic acid; Lysteda) use within 14 days of enrollment
5. Known acquired bleeding disorder
6. Known severe bleeding disorder (participants with mild von Willebrand disease will be eligible to participate in the study)
7. Use of anticoagulants (i.e. Warfarin, Coumadin, etc.) including platelet inhibitors for 14 days prior to enrollment
8. Use of prescriptive pain medications and/or use of the following analgesics: Aspirin, naproxen (Aleve), or magnesium salicylate (Doan's) during the study
9. Use of the copper intrauterine device within the past three months
10. Structural cause of heavy menstrual bleeding (e.g. fibroids, polyps, etc.) in medical records
11. Documented thrombocytopenia within the last 12 months (platelet count ≤100,000 per microliter of blood) in medical records
12. Any use of continuous hormone therapies (e.g., IUD, etc.) within three months prior to enrollment
13. Use of hormone therapies that have not followed a standard 21/7 dosing regimen for at least six months prior to enrollment
14. Participant has a history of chronic tobacco use or has ingested nicotine via smoking, vaping, smokeless tobacco, or nicotine patches in the past three months
15. Participant has a history of epileptic seizures within the past 12 months
16. Participant has a history of neurologic diseases (i.e. stroke, brain tumor, cerebrovascular, etc.)
17. Participant has a history traumatic brain injury within the past 12 months
18. Participant has had a splenectomy
19. Participant has presence of devices (e.g., pacemakers, cochlear prostheses, neurostimulators) and/or uses other neurostimulators
20. Participant has abnormal ear anatomy or ear infection present
21. Participant has previously used auricular neurostimulation for any clinical indication
22. Participant is currently or plans to be enrolled in another clinical trial during enrollment
23. Participant is a ward of the state
24. Participant has any other significant disease or disorder which, in the opinion of the Investigator, may either put the participants at risk because of participation in the trial, or may influence the result of the trial, or the participant's ability to participate in the trial

Regularly menstruating females.

Principal Investigator, Co-Investigators, study coordinators, and biostatisticians will be blinded to treatment group.