Important Information

  • FDA warning This drug has a Black Box Warning. This is the most serious warning from the Food and Drug Administration (FDA). A black box warning alerts doctors and patients to potentially dangerous effects.
    Potentially fatal heart risks. Mefenamic acid may increase your risk of heart problems, including heart attack, stroke, heart failure, or blood clot. These conditions can be fatal. Your risk may increase if you already have heart disease or have taken the medication for a long period of time or at high doses.
    You shouldn’t take mefenamic acid to treat pain before a coronary bypass graft surgery. This is a heart surgery that’s done to increase blood flow to your heart. Taking mefenamic acid around the time of your surgery will increase your risk of heart attack and stroke.
    Potentially fatal stomach problems: Mefenamic acid may increase your risk of stomach problems, such as bleeding, or small holes in the lining of your stomach or intestines (peptic ulcers). These conditions can be fatal. They can occur at any time and without any warning signs or symptoms. If you’re aged 65 years or older, you may have a greater chance for severe stomach issues.
  • May cause liver damage: Mefenamic acid may damage your liver. Your doctor may take a blood test to monitor your liver and make sure this drug is safe for you. Call your doctor immediately if you notice symptoms of liver damage, such as:
    • nausea
    • tiredness
    • itching
    • yellowing of your skin or whites or your eyes
    • pain in your upper stomach
    • flu-like symptoms, such as fever, chills, and body aches
  • Dangerous skin reactions: Get emergency medical help right away if you experience:
    • a severe skin reaction
    • rash that is red, swollen, peeling, or blistered
    This might be a severe skin disorder such as exfoliative dermatitis, Stevens-Johnson syndrome, or toxic epidermal necrolysis, which can be fatal.
  • Pregnancy warning: You shouldn’t use mefenamic acid in the third trimester of pregnancy. It may cause the blood vessel that supplies nutrients and oxygen to the fetus to close too early

Drug Features

Mefenamic acid is a prescription medication. It’s available as an oral capsule. It’s also available in a generic version. Generic drugs usually cost less. In some cases they may not be available in every strength or form as the brand. Talk to your healthcare provider to see if the generic will work for you.

Why It's Used

Mefenamic acid is used to treat mild to moderate pain and menstrual cramps. It’s approved to treat pain in people who are least 14 years old for no longer than 7 days. It’s approved to treat menstrual cramps for no longer than 2–3 days.

How It Works

Mefenamic acid belongs to a class of drugs called nonsteroidal anti-inflammatory drugs (NSAIDs). NSAIDs help reduce pain, inflammation, and fever.

It isn’t known how this medication works to decrease pain. It may help reduce swelling by lowering levels of prostaglandin, a hormone-like substance that usually causes inflammation.

MOST COMMON SIDE EFFECTS

The most common side effects that occur with mefenamic acid include:

  • stomach pain
  • nausea
  • vomiting
  • heartburn
  • constipation
  • diarrhea
  • rash
  • dizziness
  • ringing in your ear (tinnitus)

Mild side effects may go away within a few days or a couple of weeks. Talk to your doctor or pharmacist if they’re more severe or don’t go away.

SERIOUS SIDE EFFECTS

If you experience any of these serious side effects, call your doctor right away. If your symptoms are potentially life threatening or if you think you’re experiencing a medical emergency, call 9-1-1.

  • heart attack or stroke. Symptoms may include:
    • chest pain
    • shortness of breath
    • weakness on one side of your body
    • slurred speech
  • heart failure. Symptoms may include:
    • unusual weight gain
    • swelling in your arms, legs, hands, or feet
  • stomach problems, such as ulcers or bleeding. Symptoms may include:
    • stomach pain or upset stomach
    • black, sticky stools
    • vomiting up blood
  • liver problems. Symptoms may include:
    • yellowing of your skin or whites of your eyes
    • flu-like symptoms, such as fever, chills, and body aches
    • tiredness
    • nausea
    • pain in the upper part of your stomach
    • itching
  • skin reactions. Symptoms may include:
    • reddening, blistering, or peeling skin
  • allergic reactions. Symptoms may include:
    • shortness of breath
    • swelling of your face, lips, or throat

Mefenamic acid may interact with other medications, herbs, or vitamins you might be taking. That’s why your doctor should manage all of your medications carefully. If you’re curious about how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Note: You can reduce your chances of drug interactions by having all of your prescriptions filled at the same pharmacy. That way, a pharmacist can check for possible drug interactions.

Alcohol Interaction

Combining alcohol with mefenamic acid increases your risk of stomach bleeding or ulcer.

Medications That Might Interact with This Drug

Blood pressure drugs

  • angiotensin-converting enzyme (ACE) inhibitors

Mefenamic acid may decrease the blood pressure-lowering effects of ACE inhibitors.

Diuretics (water pills)

Mefenamic acid can decrease the effectiveness of medications used to get rid of extra fluid in your body.

Nonsteriodal anti-inflammatory drugs

These include:

  • aspirin
  • ibuprofen
  • naproxen

Combining these medications may increase your risk of stomach bleeding and ulcers.

Anticoagulant, blood thinner

  • warfarin

Taking both medications together increases your risk for serious stomach bleeding.

Bipolar disorder drug

  • lithium

Mefenamic acid may increase the amount of lithium in your body, which could be toxic. Your doctor may monitor for signs of lithium poisoning, such as nausea, vomiting, diarrhea, tremors, or confusion.

Disease-modifying antirheumatic drug

  • methotrexate

Mefenamic acid may increase the amount of methotrexate in your body, which may increase side effects of methotrexate.

Antacid

  • magnesium hydroxide (milk of magnesia)

Magnesium hydroxide may increase mefenamic acid levels in your body, which could increase its side effects.

Mefenamic acid Warnings

  • People with heart disease: This includes heart failure and high blood pressure. Mefenamic acid may cause an increased risk of heart problems, including heart attack, stroke, or blood clot. Your risk may be higher if you already have heart disease and take the medication for a longer period of time. Mefenamic acid may cause you to retain water and can make high blood pressure worse or increase your risk of heart failure.
  • People with ulcers and stomach bleeding: Mefenamic acid increases your risk of bleeding or ulcers in your stomach or intestines. These can occur at any time and without any warning signs or symptoms. You’re at a greater risk for serious stomach and intestinal bleeding if you’re older than 65 years, drink alcohol, or smoke cigarettes. Tell your doctor if you currently have stomach ulcer or bleeding, or if you’ve had one in the past
  • People with asthma: Mefenamic acid may cause your airways to become narrower or smaller, which can be deadly. If your asthma gets worse, get emergency medical help. If you have asthma that’s sensitive to aspirin or NSAIDs, you shouldn’t take this medication at all.
  • People with kidney disease: Mefenamic acid can damage your kidneys if you take it for a long period of time. Tell your doctor if you have a history of kidney disease.
  • Pregnant women: Mefenamic acid is a category C pregnancy drug. That means two things:
    1. Research in animals has shown adverse effects to the fetus when the mother takes the drug.
    2. There haven’t been enough studies done in humans to be certain how the drug might affect the fetus.
    You shouldn’t take mefenamic acid in the third trimester of pregnancy. It may cause the blood vessel that supplies nutrients and oxygen to the fetus to close too early.
    Speak with your doctor if you’re pregnant or plan to become pregnant. Mefenamic acid should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
  • Women who are nursing: Small amounts of mefenamic acid may be passed into your breast milk and cause side effects in your child.
    You and your doctor may need to decide whether you’ll stop breastfeeding or stop taking mefenamic acid.
  • For Seniors: If you’re older than 65 years, your body may clear this drug more slowly. This can lead to a build up of the drug in your body and increase your risk of side effects. Your doctor may monitor your kidneys while you take mefenamic acid to make sure it’s still safe for you.
  • For Children: The safety and effectiveness of mefenamic acid haven’t been established in people younger than 14 years.
  • Allergies: Mefenamic acid can cause a severe allergic reaction. Symptoms may include:
    • trouble breathing
    • swelling of your face or throat
    • hives
    Don’t take this drug again if you’ve ever had an allergic reaction to it. Taking it again could be fatal.
    Don’t take this medication if you’re allergic to aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs). These include ibuprofen, naproxen, diclofenac, and meloxicam.

All possible dosages and forms may not be included here. Your dose, form, and how often you take it will depend on:

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

What Are You Taking This Medication For?

Mild to moderate pain

Form: Oral Capsule
Strength: 250 mg

Adult Dosage (ages 18 years and older)
The first dose is 500 mg. After that, take 250 mg every 6 hours as needed. You shouldn’t take mefenamic acid for longer than 7 days.

Child Dosage (ages 14-17 years)
The first dose is 500 mg. After that, take 250 mg every 6 hours as needed. You shouldn’t take mefenamic acid for longer than 7 days.

Child Dosage (ages 0-13 years)
Dosage for people younger than 14 years hasn’t been established.

Special considerations
Liver problems: If you have liver disease, your body might not be able to process this drug well. This may cause increased amounts of mefenamic acid in your blood and increase your risk of side effects. Your doctor may decrease your dose.

Kidney problems: If you have kidney disease, your body might not be able to clear out this drug as well as it should. This may cause increased amounts of mefenamic acid in your blood and increase your risk of side effects. Your doctor may decrease your dose.

Menstrual pain

Form: Oral Capsule
Strength: 250 mg

Adult Dosage (ages 18 years and older)

  • Start this medication when your bleeding and symptoms start.
  • The first dose is 500 mg. After that, take 250 mg every 6 hours as needed.
  • You shouldn’t take mefenamic acid for longer than 3 days.

Child Dosage (ages 14-17 years)

  • Start this medication when your bleeding and symptoms start.
  • The first dose is 500 mg. After that, take 250 mg every 6 hours as needed.
  • You shouldn’t take mefenamic acid for longer than 2–3 days.

Child Dosage (ages 0-13 years)
Dosage for people younger than 14 years hasn’t been established.

Special considerations
Liver problems: If you have liver disease, your body might not be able to process this drug well. This may cause increased amounts of mefenamic acid in your blood and increase your risk of side effects. Your doctor may decrease your dose.

Kidney problems: If you have kidney disease, your body might not be able to clear out this drug as well as it should. This may cause increased amounts of mefenamic acid in your blood and increase your risk of side effects. Your doctor may decrease your dose.

Important Considerations for Taking Mefenamic acid

  • You can take mefenamic acid with food to avoid upset stomach.
  • Don’t crush or chew the oral capsule. Swallow it whole.
  • Store mefenamic acid at room temperature: 68–77°F (20–25°C). Keep it in the container given to you at the pharmacy, and keep it tightly closed. Keep your drugs away from areas where they could get wet, such as bathrooms. Store them away from moisture and damp locations.
  • This prescription is refillable.
  • When traveling with your medication:
    • Always carry it with you or in your carry-on bag.
    • Don’t worry about airport X-ray machines. They can’t hurt this medication.
    • You may need to show your pharmacy’s preprinted label to identify the medication. Keep the prescription-labeled box with you when traveling.
  • Your doctor may perform:
    • blood tests to check for possible bleeding
    • liver function tests to make sure mefenamic acid isn’t harming your liver
    • kidney function tests to make sure mefenamic acid isn’t harming your kidneys
  • Not every pharmacy stocks this drug, so call ahead
  • Many insurance companies will require a prior authorization before they approve the prescription and pay for mefenamic acid.

Are There Any Alternatives?

There are other drugs available to treat your condition. Some may be more suitable for you than others. Talk to your doctor about possible alternatives.