Mefenamic acid is a prescription pain reliever often used for period pain and heavy periods. Here’s what it is, the common and serious side effects, who should avoid it, and how it compares with ibuprofen.
Mefenamic acid (brand names Ponstel in the US and Ponstan in the UK and elsewhere) is a nonsteroidal anti-inflammatory drug, or NSAID, in the same family as ibuprofen and naproxen. It lowers prostaglandins, the chemicals that make the uterus cramp, so it’s used for period pain and, in many countries, for heavy periods. It’s prescription-only in the US and UK. The most common mefenamic acid side effects are stomach upset, diarrhea, nausea, heartburn, dizziness and headache. Like all NSAIDs, it can rarely cause stomach bleeding, kidney problems, and heart attack or stroke. It’s meant for short courses, usually just the first few days of your period, taken with food.
Common side effects
- Stomach upset, including stomach pain, indigestion, heartburn, gas and nausea. Taking it with or right after food helps.
- Diarrhea. More common with mefenamic acid than with some other NSAIDs. Stop taking it and call your doctor if you get diarrhea.
- Constipation or loss of appetite.
- Dizziness, drowsiness or headache. Don’t drive if you feel dizzy or sleepy.
- Mild rash or itching.
- Ringing in the ears or fluid retention (swollen ankles), especially with higher doses.
Avoid alcohol while taking it, since alcohol and smoking can make stomach side effects worse.
Serious side effects: stop and get help
- Stomach or gut bleeding: black, tarry or bloody stools, vomiting blood or what looks like coffee grounds, or severe stomach pain.
- Allergic reaction: swelling of the face, lips or throat, wheezing, trouble breathing, or hives. Call 911.
- Heart attack or stroke warning signs: chest pain, shortness of breath, sudden weakness on one side, slurred speech. Call 911.
- Serious skin reaction: blistering, peeling or a spreading rash, often with fever.
- Kidney problems: passing much less urine, blood in the urine, or new swelling.
- Liver problems: yellow skin or eyes, dark urine, pale stools.
- Blood problems (rare): unusual bruising or bleeding, sore throat and fever, or unusual tiredness and paleness.
Taking more than prescribed can cause serious harm, including seizures. If you’ve taken too much, call Poison Control (1-800-222-1222 in the US) or seek emergency care.
Who should avoid it or check first
- Anyone who has had a stomach ulcer or stomach bleeding, or has Crohn’s disease or ulcerative colitis.
- Anyone with kidney or liver disease, heart disease, heart failure or high blood pressure, or right before or after heart bypass surgery.
- Anyone whose asthma or breathing gets worse with aspirin or other NSAIDs.
- People who are pregnant, trying to conceive, or breastfeeding. NSAIDs are generally avoided later in pregnancy.
- Anyone taking blood thinners, aspirin, other NSAIDs, steroids, certain antidepressants (SSRIs and SNRIs), lithium, methotrexate, or blood pressure medicines such as ACE inhibitors and diuretics.
Never take mefenamic acid together with ibuprofen, naproxen or another NSAID. Ask your pharmacist about anything else you take, including supplements.
Mefenamic acid vs ibuprofen
Both work the same way, by lowering prostaglandins. A Cochrane review of NSAIDs for period pain found they all work well and found little good evidence that any one NSAID is better than another. Mefenamic acid is sometimes chosen when heavy bleeding is also a problem, since it can reduce blood loss. Ibuprofen is available without a prescription, is cheaper, and is often tried first; see Ibuprofen for Period Cramps. If one NSAID doesn’t help, your doctor may suggest another, or hormonal options; see Birth Control for Period Cramps.
NSAIDs work best started at the first sign of your period or pain, and taken for only the days you need them. Follow the dose and number of days on your prescription.
When to see a doctor about your period pain
If you need a prescription pain reliever every month, or it doesn’t control your pain, it’s worth asking why. Pain that gets worse year by year, pain outside your period, pain during sex, or very heavy bleeding can be signs of endometriosis or adenomyosis. Heavy bleeding with large clots is worth checking too; see Blood Clots During Your Period.
The traditional Chinese medicine view
In Traditional Chinese Medicine, period pain that eases with warmth, with dark blood or clots and cold hands and feet, is traditionally linked to cold in the uterus. Traditional self-care keeps the lower belly and feet warm and favors warm, cooked food during your period. This is a traditional framework, not an established medical mechanism; see Feeling Cold During Your Period.
The CycleCalm herbal pouch follows that tradition and is worn over the navel for familiar monthly cramps and discomfort. It’s not a pain medicine and not a treatment for any medical cause of period pain. Never stop or change a prescribed medicine without talking to your doctor.
Quick answers
What is mefenamic acid used for?
It’s a prescription NSAID used for short-term pain, most often period pain, and in many countries for heavy periods.
What are the most common side effects of mefenamic acid?
Stomach upset, diarrhea, nausea, heartburn, dizziness and headache. Stop and call your doctor if you get diarrhea.
Is mefenamic acid stronger than ibuprofen?
Not clearly. Research hasn’t shown one NSAID to be better than another for period pain; the best choice depends on you.
Can I take mefenamic acid with ibuprofen?
No. Taking two NSAIDs together raises the risk of stomach bleeding and kidney problems without adding much relief.
Reviewed October 2026. Author: Qingcai Wang, MD, PhD, developer of the Five Essences external herbal-pouch formulations, with a commercial interest in their sale. General education only; continue your medical care.
Sources: Mefenamic Acid 500 mg Tablets, patient information leaflet (emc); Drugs.com, Mefenamic acid side effects; Cochrane, NSAIDs for dysmenorrhoea.