The goal of this clinical trial is to determine if transauricular vagal nerve stimulation (taVNS) is effective in treating moderate dysmenorrhea. The main question it aims to answer is:

• Does taVNS reduce the number of times participants suffering from dysmenorrhea need to use rescue medication during menstruation? Researchers will compare taVNS stimulation with a sham stimulation (a look-alike procedure that does not stimulate the vagus nerve) to assess whether taVNS is effective in treating moderate dysmenorrhea.

Participants will:

• Undergo taVNS for 2 months and sham stimulation for another 2 months, each for 5 days per month, starting 2 days before the expected beginning of their menstrual cycle.
• Visit the clinic twice a month for checkups and tests.
• Keep a diary to record their pain levels and the number of times they use rescue medication.
• Undergo functional magnetic resonance imagine two times (one after the end of the first use of taVNS and another after the end of the first use of SHAM stimulation).

Inclusion Criteria:

• Regular menstrual cycle (28 days ± 7 days);
• Average moderate menstrual pain (with 4 - 7 NRS scores);
• History of over-the-counter (OTC) analgesic use for the treatment of menstrual pain (at least 1 IBUPROFEN for the first two days);
• 4 consecutive monthly menstrual cycles;
• Non-pregnant status;
• Agrees to use adequate birth control during the trial;
• Otherwise, healthy;
• Agree not to participate in any other clinical trial while enrolled in this trial ;
• No facial or ear pain, no recent ear trauma, no metal implants including pacemakers;
• Normal ECG, Heart Rate and Blood Pressure (systolic BP 105-130, diastolic BP 60-90, heart rate per min at rest 60-85);

Exclusion Criteria:

• Currently under medications (except for analgesic medication for menstrual cycle);
• Use of oral contraceptive;
• Secondary cause for dysmenorrhea (i.e., endometriosis, adenomyosis, uterine fibroids, or infection);
• Unstable or serious illness (e.g., kidney, liver, GIT, heart conditions, diabetes, thyroid gland function, lung conditions, chronic asthma, diagnosed psychological or mood disorder, hypertension, any bleeding disorders, recent surgery, or concurrent blood thinning treatment);
• Current malignancy or treatment for malignancy within the previous 2 years;
• Pregnant or lactating women;
• Active smokers, nicotine use, or drug (prescription or illegal substances) abuse;
• Chronic past and/or current alcohol use (>14 alcoholic drinks per week);
• Any condition that in the opinion of the investigator, makes the participant unsuitable for inclusion;
• Unwilling or unable to comply with protocol;
• Active genitourinary infection in the last four weeks;
• Unable to read or comprehend the informed consent;
• Unwilling to complete study procedures;
• Participated in any other clinical trial during the past 1 month;
• Personal or family history of seizure, mood, or cardiovascular disorders;
• Allergic reaction to surface electrodes.

Female

Primary and secondary outcomes

IPD will be available at the end of the relevant analyses with not limit of time.

IPD will be available on the platform OSF