Mefenamic Acid for Period Pain: The Dual-Action Option
The prescription NSAID that reduces both pain and heavy bleeding — how it works, who it suits and when to choose it.
Part of the Access Doctor period pain guide.
Key fact: Mefenamic acid is the only commonly prescribed NSAID for period pain that has a dual mechanism — it both inhibits prostaglandin synthesis (like ibuprofen and naproxen) and directly blocks prostaglandin receptors. It also reduces menstrual blood loss by 20–30%, making it the preferred choice for women with both painful and heavy periods.
Get Prescription Pain Relief Online
Access Doctor GPhC-registered pharmacist independent prescribers can prescribe naproxen 500mg and ibuprofen 600mg for period pain online. No GP appointment needed. Next-working-day delivery.
Start Consultation →How Mefenamic Acid Works
Mefenamic acid belongs to the fenamate class of NSAIDs and has two distinct actions relevant to period pain:
- COX inhibition — like ibuprofen and naproxen, it inhibits both COX-1 and COX-2 enzymes, reducing the synthesis of prostaglandins from arachidonic acid. This reduces the total prostaglandin load in the uterus.
- Prostaglandin receptor antagonism — uniquely, mefenamic acid also directly blocks prostaglandin receptors, limiting the effect of prostaglandins already present. This dual blockade provides additional pain relief compared to COX inhibition alone.
Additionally, mefenamic acid reduces menstrual blood loss by approximately 20–30% through its effects on prostaglandin-mediated platelet aggregation and uterine vasodilation. This makes it particularly valuable when period pain and heavy bleeding occur together.
Correct Dose and Timing
| Dose | Timing | Duration | Notes |
|---|---|---|---|
| 500mg three times daily | Every 8 hours with food | For the painful days (2–3 days) | Standard prescription dose; max 1,500mg/day |
As with all NSAIDs for period pain: start at the first sign of bleeding or pain. The earlier treatment begins, the more effectively it limits prostaglandin levels before they peak. Always take with food.
Mefenamic acid is prescription only in the UK. Unlike ibuprofen 400mg or naproxen 250mg, there is no OTC formulation. Access Doctor prescribers can assess suitability and prescribe online following a short consultation.
Who Mefenamic Acid Suits Best
Painful + heavy periods
The dual prostaglandin-reducing mechanism addresses both components simultaneously. First-line NSAID choice when both are problematic.
Inadequate response to ibuprofen/naproxen
The additional prostaglandin receptor blockade gives mefenamic acid a different mechanism that may work better for some women who have not responded to standard NSAIDs.
Secondary dysmenorrhoea (e.g. endometriosis)
In endometriosis-related dysmenorrhoea, prostaglandin activity may be higher than in primary dysmenorrhoea. The receptor-blocking component may provide additional relief.
Mefenamic Acid vs Ibuprofen vs Naproxen
| Feature | Mefenamic acid 500mg | Ibuprofen 600mg | Naproxen 500mg |
|---|---|---|---|
| Mechanism | COX inhibition + prostaglandin receptor block | COX inhibition | COX inhibition |
| Reduces heavy bleeding? | Yes (~20–30%) | Modest | Modest |
| Doses per day | 3 (every 8h) | 3 (every 6–8h) | 2 (every 8–12h) |
| Prescription required? | Yes — prescription only | OTC at 400mg; Rx at 600mg | OTC at 250mg; Rx at 500mg |
| Best for | Painful + heavy periods; NSAID non-responders | Quick relief; flexible dosing | Sustained all-day relief; fewer doses |
Side Effects and Precautions
- GI symptoms — nausea, diarrhoea, heartburn; common; take with food. Diarrhoea is slightly more common with mefenamic acid than other NSAIDs.
- Headache, dizziness — mild; usually transient
- Haemolytic anaemia — rare; more associated with long-term use. For short 2–3 day courses per cycle, clinically insignificant for most women.
Contraindicated in the same circumstances as all NSAIDs: peptic ulcer disease, significant kidney impairment, aspirin-sensitive asthma, third trimester pregnancy, severe heart failure. Mefenamic acid is additionally not recommended in inflammatory bowel disease.
Get Prescription Pain Relief Online
Access Doctor GPhC-registered pharmacist independent prescribers can prescribe naproxen 500mg and ibuprofen 600mg for period pain online. No GP appointment needed. Next-working-day delivery.
Start Consultation →Frequently Asked Questions
What is mefenamic acid and how is it different from other NSAIDs?
Mefenamic acid has a dual mechanism: COX inhibition (like ibuprofen/naproxen) plus direct prostaglandin receptor blockade. It also reduces menstrual blood loss by 20–30%. Prescription only in the UK.
What is the dose of mefenamic acid for period pain?
500mg three times daily with food, starting at the onset of pain or bleeding. Continue for 2–3 painful days. Maximum 1,500mg/day.
Can mefenamic acid reduce heavy periods as well as pain?
Yes — reduces blood loss by approximately 20–30% alongside pain relief. First-line NSAID choice for women with both painful and heavy periods.
Is mefenamic acid stronger than ibuprofen or naproxen?
Different rather than simply stronger. Its additional prostaglandin receptor blockade may benefit women who have not responded to ibuprofen or naproxen, and its blood-loss reduction is unique among common NSAIDs.
Who should use mefenamic acid instead of ibuprofen or naproxen?
Women with both pain and heavy bleeding, inadequate response to ibuprofen or naproxen, or secondary dysmenorrhoea (e.g. endometriosis).
References
- National Institute for Health and Care Excellence (NICE). Heavy menstrual bleeding: assessment and management (NG88). 2018 (updated 2023). nice.org.uk/guidance/ng88
- Marjoribanks J et al. Nonsteroidal anti-inflammatory drugs for dysmenorrhoea. Cochrane Database Syst Rev. 2015. PubMed: 26224322
- NHS. Mefenamic acid. nhs.uk/medicines/mefenamic-acid
Medical disclaimer: This article is for informational purposes only. Period pain can be a symptom of an underlying condition requiring assessment. In an emergency call 999.