Spark Biomedical, a Dallas-based medical device developer, has launched a Phase II randomised, double-blind, sham-controlled clinical trial evaluating transcutaneous auricular neurostimulation (tAN) as a non-pharmacological treatment for heavy menstrual bleeding. The LUNA trial, enrolling 80 participants aged 14 to 45 across U.S. sites affiliated with Oregon Health and Science University, the University of Michigan, and Yale University, represents the first placebo-controlled study of the technology in this indication. The trial is backed by Pathway to Cures, the venture philanthropy arm of the National Bleeding Disorders Foundation, and funded in part by the Wellcome Leap Missed Vital Sign programme.

Why a sham-controlled design matters for a wearable device in gynaecology

The LUNA trial’s design choice is arguably its most consequential feature. Demonstrating efficacy for a wearable neurostimulation device requires convincing participants and investigators that a sham condition is indistinguishable from active treatment. For transcutaneous electrical devices, this is technically achievable but scientifically demanding. Placebo response rates in pain and symptom-burden studies are substantial, and heavy menstrual bleeding endpoints measured by patient-reported pictorial blood loss assessment charts introduce further subjectivity. The degree to which Spark Biomedical can maintain blinding integrity across five menstrual cycles will be a key determinant of whether the trial produces data regulators can act on.

The move to a controlled design is also a direct response to the limitations of the predecessor study. A pilot trial conducted between October 2023 and April 2025 and subsequently published in Frontiers in Medicine enrolled 16 participants in an open-label, two-arm format. That study reported an average reduction in menstrual blood loss exceeding 50% among device users, alongside improvements in cramping, fatigue, and quality of life. Clinicians tracking the field have noted that while these results were directionally encouraging, the absence of a sham comparator made it impossible to separate the device’s physiological effect from participant expectation. The LUNA trial is designed to resolve precisely that question.

What the mechanism proposes and where the science remains uncertain

The tAN approach targets the auricular branch of the vagus nerve and the auriculotemporal nerve through the outer ear, stimulating both pathways non-invasively. The proposed mechanism of action draws on preclinical evidence that vagus nerve stimulation modifies platelet phenotype and can reduce blood loss in soft tissue injury models. Translating that haemostatic mechanism to menstrual physiology is not straightforward. Menstrual blood loss is regulated by a distinct set of local endometrial processes, including prostaglandin signalling, fibrinolytic activity, and vascular tone, rather than by systemic coagulation alone. The degree to which peripheral vagal stimulation delivered through the ear influences endometrial haemostasis in humans remains a genuinely open question, and the LUNA trial will need to produce a plausible effect size to justify further development.

The device also stimulates the auriculotemporal nerve, a branch of the trigeminal system, which the company positions as a differentiating feature compared with conventional transcutaneous vagus nerve stimulation devices. Regulatory watchers suggest that dual-pathway stimulation adds mechanistic complexity that will require careful characterisation in any eventual regulatory submission, particularly if Spark Biomedical seeks a de novo or 510(k) pathway for this indication rather than positioning the technology as a wellness device only.

Inclusion of von Willebrand disease patients shifts the trial’s strategic logic

The LUNA trial’s inclusion of women and girls diagnosed with von Willebrand disease adds a medically and commercially significant dimension to the study. Von Willebrand disease is the most common inherited bleeding disorder and heavy menstrual bleeding is frequently its most burdensome clinical manifestation. According to data from the National Bleeding Disorders Foundation’s Community Voices in Research registry, 46% of women with a bleeding disorder report missing school or work because of heavy menstrual bleeding. Existing treatment options for this population are constrained: hormonal therapies carry contraindications or are declined on personal grounds, tranexamic acid provides partial relief, and desmopressin and clotting factor concentrates are not universally effective across von Willebrand disease subtypes.

A non-pharmacological device that demonstrates efficacy in a von Willebrand disease subgroup would address a genuine clinical gap for which no currently approved device exists. The trial is not, however, powered to demonstrate efficacy specifically in that subgroup, and any von Willebrand disease-specific claims from LUNA data would require a separate, adequately powered study. Industry observers note that the inclusion nonetheless positions Spark Biomedical for a targeted label expansion strategy if the main trial succeeds, given the existing collaborative infrastructure with the National Bleeding Disorders Foundation and the three academic medical centres already engaged.

How this positions Spark Biomedical against existing treatment standards

Heavy menstrual bleeding is one of the most common reasons for gynaecological referral globally, yet the treatment landscape has not fundamentally changed in decades. First-line approaches include the levonorgestrel intrauterine system, combined oral contraceptives, tranexamic acid, and non-steroidal anti-inflammatory drugs. Surgical options such as endometrial ablation and hysterectomy remain the last resort but carry procedural risks and, in the case of ablation, are contraindicated in women who wish to preserve fertility. For adolescents, in particular, the prescribing space is further constrained by age, fertility considerations, and parental preference, which is likely why the LUNA trial has specifically created a 14-to-21 cohort separate from the adult arm.

Spark Biomedical’s OhmBody device is already on the market as a wellness product, positioned as a non-invasive, hormone-free wearable that supports menstrual symptom relief. That positioning does not require clinical evidence to the same evidentiary standard as a regulated medical device. The LUNA trial is structurally different: it is designed to generate the clinical data that could support a regulated device claim. Whether the company intends to pursue a de novo classification for a menstrual blood loss indication, or whether a successful Phase II will be used primarily to strengthen OhmBody’s commercial positioning and justify further investment, is not yet publicly stated.

Decentralised trial structure reduces barriers but creates data quality considerations

The fully decentralised design, in which all study activities occur remotely, addresses a long-standing structural problem in menstrual health research: participation barriers related to geography, scheduling, and the social stigma that still surrounds discussion of menstruation in clinical settings. The Wellcome Leap Missed Vital Sign programme, which is co-funding the trial, has explicitly stated a goal of reducing the time from symptom onset to effective treatment for heavy menstrual bleeding from roughly five years to five months. A decentralised model that enrols across multiple geographies simultaneously is consistent with that ambition. Participants will self-administer a two-hour daily neurostimulation session during menstruation and track blood loss using validated pictorial assessment tools remotely.

The data quality risks in a decentralised study of this kind are not trivial. Remote self-administration introduces device usage compliance variability that on-site administration would eliminate. Pictorial blood loss assessment, while validated, relies on participant interpretation and is subject to recall and scoring inconsistency, particularly in an adolescent cohort. The two-cycle baseline period before treatment begins is a methodologically sound design choice that provides each participant with an internal control, but it also extends total trial duration to approximately five months per participant. Dropout rates over that period will be a meaningful trial execution risk.

What a Phase II result would and would not resolve for the field

Regulatory watchers suggest the LUNA trial, if successful, would establish proof of concept in a controlled setting and likely support a Phase III submission rather than a direct regulatory authorisation pathway. An 80-participant study is sufficient to detect a meaningful signal but not to satisfy the safety and efficacy data threshold typically required for a new device classification in a chronic condition. The primary endpoint, the proportion of participants achieving a clinically meaningful reduction in menstrual blood loss compared to baseline, will be interpretable if the sham-controlled comparison achieves statistical significance, but the definition of clinical meaningfulness itself will require agreement with regulators before a pivotal programme can be designed.

For the broader field of bioelectronic medicine in gynaecology, LUNA represents a significant step. Neuromodulation has achieved substantial clinical adoption in neurology, pain management, and cardiac rhythm disorders, but its application in women’s reproductive health has been confined to research settings. A well-executed Phase II result in a double-blind trial would give the field its first controlled dataset on auricular neurostimulation in menstrual disorders and would clarify whether the mechanism identified in preclinical haemostasis models translates meaningfully to the clinical setting. That outcome alone would carry value beyond Spark Biomedical’s commercial trajectory.

Investment context and what the funding structure signals about near-term priorities

Spark Biomedical raised a $15 million Series A in April 2025 led by Wave Financing and subsequently received an investment from Northwell Holdings, the strategic investment vehicle of Northwell Health, the largest health system in New York. The Pathway to Cures backing for the LUNA trial adds a third capital source, structured as venture philanthropy rather than conventional equity investment. The layered funding structure suggests Spark Biomedical is managing a dual strategy: building OhmBody as a direct-to-consumer wellness business that generates commercial revenue while simultaneously running the regulated clinical programme needed to establish a prescription or cleared device claim. That is a resource-intensive position that will require careful coordination between the wellness and clinical development tracks to avoid evidence cross-contamination or regulatory ambiguity.

Clinicians and investors tracking the women’s health device sector will watch whether LUNA’s recruitment timeline stays on track and whether Spark Biomedical publicly commits to a regulatory strategy before Phase II completion. The absence of a declared U.S. Food and Drug Administration pathway creates interpretive uncertainty about the trial’s ultimate purpose. If results are positive, the company will face the credibility test of converting an encouraging 80-participant Phase II into a funded, adequately powered pivotal programme in a therapeutic area where clinical development has historically been underfunded and slow.

  bioelectronic medicine, gynaecology, heavy menstrual bleeding, LUNA trial, medical devices, menstrual health, NBDF, neuromodulation, OhmBody, Pathway to Cures, Phase II clinical trial, Spark Biomedical, transcutaneous auricular neurostimulation, von Willebrand disease, Wellcome Leap, women’s health devices