A healthy young woman on combined oral contraceptive pills presents with severe lower‑abdominal cramping that starts one day before menses and continues for two days into the period, preventing her from working despite using acetaminophen; what is the most likely diagnosis and appropriate first‑line treatment?

Primary Dysmenorrhea with Inadequate Response to Acetaminophen

This patient has primary dysmenorrhea that is inadequately controlled with acetaminophen; she should immediately switch to an NSAID (ibuprofen 400mg every 4-6 hours or naproxen 500mg twice daily) starting one day before expected menses, and if NSAIDs alone provide insufficient relief after 2-3 cycles, add combined oral contraceptives in an extended or continuous regimen to reduce or eliminate menstrual periods entirely. 1

Diagnosis: Primary Dysmenorrhea

This clinical presentation is classic for primary dysmenorrhea—cramping lower abdominal pain starting one day before menses and lasting two days into the period, severe enough to prevent work, in an otherwise healthy young woman. 2, 3, 4

• Primary dysmenorrhea is caused by increased endometrial prostaglandin production (PGF2α and PGE2), resulting in uterine hypercontractility, ischemia, and pain. 2, 3, 4
• It affects up to 90% of reproductive-age women and is the leading cause of work and school absenteeism in young women. 2, 3, 5
• The diagnosis is clinical, based on typical cramping pain timing (just before or during menses), duration (1-3 days), and normal physical examination. 3, 4, 5

Why Acetaminophen Failed

Acetaminophen has no anti-prostaglandin activity and is therefore ineffective for primary dysmenorrhea, which is a prostaglandin-mediated condition. 2, 3

First-Line Treatment: NSAIDs

NSAIDs are the mainstay of treatment because they directly inhibit prostaglandin synthesis at the endometrium. 1, 2, 3, 4

• Start ibuprofen 400mg every 4-6 hours OR naproxen 500mg twice daily beginning one day before expected menses and continue through the first 2-3 days of bleeding. 1
• Starting NSAIDs before pain onset (prophylactically) is more effective than waiting until pain begins, as it prevents prostaglandin accumulation. 2, 3
• NSAIDs provide adequate relief in approximately 90% of women with primary dysmenorrhea. 2, 4

Second-Line Treatment: Combined Oral Contraceptives

If NSAIDs alone provide insufficient relief after 2-3 menstrual cycles, add combined oral contraceptives. 1

• COCs reduce dysmenorrhea by suppressing endometrial proliferation and prostaglandin production, with a pooled odds ratio of 2.01 (95% CI 1.32-3.08) for pain relief versus placebo. 1
• Both low-dose (20-35 μg ethinyl estradiol) and medium-dose formulations are effective. 6, 1

Extended/Continuous Regimen for Severe Cases

For severe dysmenorrhea that significantly impacts quality of life (like missing work), extended or continuous OCP regimens are particularly beneficial because they reduce or eliminate menstrual periods entirely. 7, 1

• Extended regimen: Take 21-24 days of active pills, then immediately start a new pack (skip placebo pills). 1
• This approach minimizes the number of withdrawal bleeds per year, thereby reducing the total number of painful episodes. 7, 1
• If breakthrough bleeding occurs during extended use, a planned 3-4 day hormone-free interval can be used to manage it. 7

Treatment Algorithm

1. Immediate switch: Stop acetaminophen, start NSAID (ibuprofen 400mg q4-6h or naproxen 500mg BID) one day before expected menses. 1
2. Trial period: Continue NSAID therapy for 2-3 menstrual cycles. 1
3. If inadequate response: Add combined oral contraceptives (30-35 μg ethinyl estradiol with levonorgestrel or norgestimate). 6, 1
4. For severe/disabling pain: Consider extended or continuous OCP regimen from the start to eliminate most menstrual periods. 7, 1

Important Clinical Considerations

• She is already on OCPs: The question states she is on "ocp pop" (likely combined oral contraceptives). If she is already taking standard cyclic COCs and still having severe dysmenorrhea, the solution is to switch to an extended or continuous regimen (skipping placebo weeks) rather than adding a different medication. 7, 1
• Backup contraception: When switching to extended regimens, no additional backup contraception is needed if she continues taking active pills daily. 6
• Red flags for secondary dysmenorrhea: If pain does not respond to NSAIDs plus hormonal therapy after 2-3 cycles, consider secondary causes (endometriosis, fibroids) and refer to gynecology. 2, 4, 5
• Contraindications to COCs: Screen for severe hypertension (≥160/100), migraines with aura, thromboembolism history, or thrombophilia before prescribing COCs. 6

Non-Pharmacologic Adjuncts

While NSAIDs and hormonal contraceptives are first-line, topical heat application and regular aerobic exercise can provide additional relief and have no contraindications. 3, 4, 5