Mefenamic Acid (Ponstel) for Period Pain: Uses and Risks

Mefenamic acid (brand name Ponstel) is a prescription NSAID, a nonsteroidal anti-inflammatory drug, that is approved to treat painful periods. It eases period pain by lowering the prostaglandins that make the uterus cramp, and it carries the same stomach, heart and kidney risks as other NSAIDs.

If you were offered mefenamic acid, or you are comparing period pain medicines, this guide covers how it works, how it is usually taken for period pain, the side effects, and who should not take it. Your prescriber and the label on your pack set your own dose.

What mefenamic acid is

Mefenamic acid is an NSAID that you take as a capsule by mouth. Ponstel is one brand name, and generic capsules contain 250 mg of mefenamic acid. In the US you need a prescription for it.

The US label lists two uses:

• Primary dysmenorrhea, which is period pain that no other condition causes
• Mild to moderate pain in people aged 14 and over, for no more than one week (7 days)

How it works on period pain

Before and during a period, the lining of the uterus makes chemicals called prostaglandins. They make the muscles and blood vessels of the uterus contract. Prostaglandin levels are highest on the first day of a period and fall as bleeding goes on, which is why pain tends to ease after the first few days.

Mefenamic acid blocks the COX-1 and COX-2 enzymes that the body uses to make prostaglandins. With fewer prostaglandins, menstrual cramps are less severe. In controlled trials, people with period pain who took mefenamic acid did better than with a placebo on pain, on the need for other painkillers, and on how often and how badly symptoms came.

How it is usually taken for period pain

For period pain, the label dose is 500 mg first, then 250 mg every 6 hours, starting when your bleeding and other period symptoms start. Your prescriber can change the dose and how often you take it after they see how you respond. Take it exactly as your prescription says.

Some other points help:

• Start early. NSAIDs work best at the first sign of your period or pain, and you usually need them for only 1 or 2 days.
• Take it with food. Take the capsules with food.
• Use the least you need. Use the lowest dose that works for the shortest time.
• Do not double up on NSAIDs. Do not take it with other NSAIDs such as ibuprofen or naproxen unless your doctor tells you to. Some over-the-counter cramp products contain one of these. Our guide to Midol, Pamprin and Tylenol shows what is in each.
• If you miss a dose. Take it when you remember. If it is almost time for the next dose, skip the missed one. Do not take a double dose.

If you took too much, call your doctor or Poison Help at 1-800-222-1222, or go to the nearest emergency room.

How it compares with other NSAIDs

Across trials, NSAIDs as a group eased period pain better than a placebo or paracetamol (acetaminophen). The same trials found little evidence that any one NSAID is better than the others for pain relief or for safety. So mefenamic acid is one choice among several, not a stronger class of medicine.

In the UK, a GP may suggest naproxen, flurbiprofen or mefenamic acid for severe period pain. If you want to compare the two common over-the-counter options, see ibuprofen or naproxen for period cramps.

Common side effects

The most common side effects of mefenamic acid include:

• Stomach pain, indigestion and heartburn
• Nausea and vomiting
• Diarrhea or constipation
• Gas
• Headache and dizziness
• Swelling
• Itching or a rash
• Ringing in the ears

Some of these, such as nausea, diarrhea, stomach pain and itching, are also on the label's list of signs to stop the capsules and call your healthcare provider right away. If you get them, stop and call. Your provider can tell you whether it is safe to go on.

Serious side effects

Mefenamic acid has a boxed warning on its US label, as other prescription NSAIDs do. NSAIDs can raise the risk of a heart attack or stroke, and this risk can start early in treatment. They can also cause bleeding, ulcers and tears in the stomach or intestines, at any time and with no warning signs. Higher doses and longer use raise both risks.

Other serious side effects include:

• Liver problems, including liver failure
• Kidney problems, including kidney failure
• New or worse high blood pressure
• Heart failure
• A high blood potassium level
• Serious skin reactions
• Life-threatening allergic reactions
• Asthma attacks in people who have asthma
• Low red blood cells (anemia)

Who should not take mefenamic acid

Do not take mefenamic acid if you:

• Are allergic to mefenamic acid or to any ingredient in the capsules
• Have had an asthma attack, hives or another allergic reaction after aspirin or another NSAID
• Are about to have, or just had, heart bypass surgery

Avoid it after a recent heart attack unless your provider tells you to take it. People with bleeding disorders, asthma, aspirin allergy, liver damage, stomach disorders or ulcers should not take NSAIDs.

Before you start, tell your healthcare provider if you have heart problems, bleeding problems, ulcers, liver or kidney problems, high blood pressure or asthma. Tell them about every medicine, vitamin and herbal supplement you take, because some can interact with mefenamic acid. The risk of a stomach ulcer or bleed is also higher if you smoke, drink alcohol or have had a stomach ulcer or bleed before.

Pregnancy, fertility and breastfeeding

• Pregnancy. Taking mefenamic acid at about 20 weeks of pregnancy or later may harm the baby. Do not take it after about 30 weeks. Between 20 and 30 weeks, use it only if your provider says so.
• Trying to get pregnant. NSAIDs, including mefenamic acid, can delay ovulation and cause infertility that goes away when you stop. If you are trying to conceive, or you are having fertility tests, ask your provider whether you should stop it.
• Breastfeeding. Mefenamic acid passes into breast milk in low amounts. Talk to your provider about how to feed your baby while you take it.

If NSAIDs do not help your period pain

Period pain from a condition such as endometriosis or fibroids is called secondary dysmenorrhea. It tends to get worse over time, it can start a few days before your period, and it may not go away when your period ends. If NSAIDs do not control your pain, or your period pain stops you doing your usual daily activities, see a doctor. To compare the patterns, read endometriosis vs normal period cramps.

When to get help

Call 911 or your local emergency number now if you have:

• Shortness of breath or trouble breathing
• Chest pain
• Weakness in one part or side of your body
• Slurred speech
• Swelling of the face or throat

These are the signs that need emergency help right away.

Stop mefenamic acid and call your healthcare provider right away if you have:

• Nausea, diarrhea, indigestion or stomach pain
• More tiredness or weakness than usual
• Itching, or yellow skin or eyes
• Vomit with blood in it, or bowel movements with blood or that are black and sticky like tar
• Unusual weight gain, or swelling of your arms, legs, hands or feet
• A skin rash or blisters with a fever
• Flu-like symptoms

These are on the label's list of symptoms to stop and call about. Also get urgent advice if your period pain is severe or worse than usual and painkillers have not helped.

What to track while you take it

A few cycles of notes show whether mefenamic acid works for you and whether the side effects are worth it. For each period, write down:

• Pain. Your worst pain from 0 to 10 before your first dose, and again later that day.
• Doses. The time of each dose, and the day of your period you started.
• Bleeding. How heavy each day was.
• Side effects. Stomach upset, diarrhea, headache, dizziness or anything new.
• Other painkillers. Anything else you took, so you do not double up on NSAIDs.

For help with the pain score, see how to describe period pain. Endolog is a free download where you log pain severity, bleeding, digestive symptoms and flare notes on the days they happen, so you have a clear record for your next appointment. A paper notebook works too.

Frequently asked questions

Is mefenamic acid stronger than ibuprofen?

There is little evidence that any single NSAID works better than another for period pain. If one NSAID does not suit you, ask your doctor whether another one might.

Can I buy mefenamic acid over the counter?

Not in the US. It is a prescription medicine. Some other NSAIDs, such as ibuprofen and naproxen, are sold over the counter.

Can I take mefenamic acid with ibuprofen?

Do not take it with ibuprofen, naproxen or other NSAIDs unless your doctor tells you to. Check the labels of any over-the-counter cramp products before you take them.

How long can I take mefenamic acid?

For period pain, you start it when your bleeding and symptoms start, and NSAIDs are usually needed for only 1 or 2 days. For other pain, the label limit is one week (7 days). Follow what your prescriber tells you.

Does mefenamic acid help endometriosis pain?

It can ease period pain. If endometriosis causes your pain, an ob-gyn may also suggest hormonal birth control or other hormone medicines. If NSAIDs are not enough, a GP may refer you to a specialist.

Related guides

• Ibuprofen or Naproxen for Period Cramps: Which and When
• Midol, Pamprin or Tylenol for Period Cramps
• What Helps Period Cramps
• Endometriosis vs Normal Period Cramps