Does Mefenamic Acid Slow Down Menstruation?
Yes, mefenamic acid reduces menstrual blood loss by approximately 20-50% and shortens the duration of menstruation in women with heavy menstrual bleeding. 1, 2
Mechanism and Efficacy
Mefenamic acid works by reducing prostaglandin synthesis, which directly decreases menstrual blood flow and endometrial inflammation. 3, 4 The evidence demonstrates:
Menstrual blood loss reduction: Mefenamic acid reduces median menstrual blood loss from 123 mL to 81 mL per cycle (a 34% reduction) in women with objectively measured menorrhagia. 2
Duration of bleeding: Treatment decreases the median number of bleeding days from 7 days to 5 days. 2
Pad count reduction: Women using mefenamic acid experience a decrease in pad usage from 23.20 to 14.33 pads per cycle. 5
Clinical Application and Dosing
Standard treatment protocol: Administer 500 mg three times daily during menstruation for 5-7 days. 1, 3, 2 This short-term regimen is recommended by the CDC as first-line therapy for:
- Heavy menstrual bleeding in women using copper IUDs 1, 6
- Breakthrough bleeding with DMPA (depot medroxyprogesterone acetate) 1
- Primary dysmenorrhea with heavy bleeding 3, 7
Comparative Effectiveness
When compared to other treatments:
Versus placebo: Mefenamic acid produces complete symptom relief in 88.6% of patients versus 13% with placebo. 7, 8
Versus other NSAIDs: No significant difference in efficacy between mefenamic acid and other NSAIDs (naproxen, indomethacin, flufenamic acid). 1, 9, 8
Versus tranexamic acid or danazol: Less effective than these agents but with fewer adverse effects. 8
Versus norethisterone: Similar efficacy in reducing menstrual blood loss (both reduced bleeding by approximately 30-40%). 2
Important Clinical Caveats
Before prescribing mefenamic acid, rule out:
- Pregnancy 4, 6
- Sexually transmitted infections 1, 6
- Structural pathology (fibroids, polyps) 1, 6
- IUD displacement (if applicable) 6
Contraindications and warnings:
- Avoid in cardiovascular disease: NSAIDs increase risk of myocardial infarction and thrombosis. 3, 4, 6
- Avoid aspirin: May paradoxically increase bleeding in women with lower baseline menstrual blood loss. 1, 6
- Use with caution: In patients with peptic ulcer disease, advanced age (>60 years), or concurrent corticosteroid therapy. 3
Treatment Limitations
Despite effectiveness, approximately 52% of women remain menorrhagic after 2 months of mefenamic acid treatment. 2 If bleeding persists and is unacceptable to the patient:
- Consider second-line hormonal therapy: Combined oral contraceptives or estrogen for 10-20 days (if medically eligible). 1, 6
- Consider alternative contraceptive methods or the levonorgestrel-releasing IUS, which reduces menstrual blood loss by 71-95%. 6
- Counsel on method switching if patient finds bleeding unacceptable. 1, 6