Mefenamic Acid for Dysmenorrhea (Period Cramps)

How it works

Mefenamic acid is an NSAID (a fenamate/anthranilic acid derivative) that non-selectively inhibits cyclooxygenase (COX), reducing prostaglandin synthesis. Primary dysmenorrhea is driven largely by excess prostaglandins causing exaggerated uterine contractions, myometrial ischemia, and pain, so cutting prostaglandin production directly targets the cause of the cramping - not just the sensation of pain - Goodman & Gilman's The Pharmacological Basis of Therapeutics; Harrison's Principles of Internal Medicine, 22nd ed.

Typical dosing

Usual regimen: 500 mg as an initial dose, then 250 mg every 6 hours.
Start dosing as soon as bleeding or cramping begins (not after pain is already severe), and continue for 2-3 days into the cycle, since prostaglandin release is highest in the first 48 hours of menses.
Labeled mainly for patients age 14+ and courses of 7 days or less.

This "start early, short course" approach is standard for all NSAIDs used in primary dysmenorrhea (ibuprofen, naproxen, ketoprofen, mefenamic acid, nimesulide) - each performs better than placebo, and there's no strong evidence one NSAID beats the others; choice often comes down to tolerability and dosing convenience - Harrison's Principles of Internal Medicine; Goldman-Cecil Medicine.

Effectiveness

NSAIDs as a class give sustained response rates above 80% in primary dysmenorrhea when used correctly (early, adequate dose) - Harrison's Principles of Internal Medicine.

Who should avoid it / cautions

Avoid or use cautiously if you:

Cannot maintain adequate hydration
Have underlying kidney disease
Are on anticoagulants, systemic steroids, lithium, or loop diuretics
Have a history of GI bleeding, coagulopathy, ischemic heart disease, stroke, heart failure, liver disease, or aspirin-sensitive asthma

Mefenamic acid specifically also raises liver enzymes in about 5% of users, so it's not ideal for anyone with existing liver problems - Goodman & Gilman's; Goldman-Cecil Medicine.

If it isn't enough

If cramps persist despite proper NSAID use, adding a combined oral contraceptive (which suppresses ovulation and lowers prostaglandin release) is the next standard step. Persistent pain despite both measures warrants evaluation for secondary causes like endometriosis or adenomyosis - Goldman-Cecil Medicine.

Recent evidence check

A quick literature check found systematic reviews/meta-analyses mostly on adjunctive or alternative therapies (fenugreek, fennel) compared against mefenamic acid as a control, not challenging its established efficacy - nothing contradicts the standard textbook guidance above (PMID: 37594100, PMID: 34187122).

Bottom line: Mefenamic acid works well for period cramps by blocking the prostaglandins that cause uterine cramping. Take it at the first sign of bleeding or cramping (500 mg then 250 mg every 6 hours) rather than waiting for pain to peak, and don't use it if you have significant kidney, liver, GI bleeding, or cardiovascular risk factors - check with a doctor or pharmacist if any of those apply to you.

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