Mefenamic acid belongs to the class of medications called nonsteroidal anti-inflammatories (NSAIDs). It is used to relieve moderately severe pain, such as muscular aches and pains, menstrual cramps, headaches, and dental pain.

Mefenamic acid relieves pain and inflammation as long as it is being taken, however it does not correct the cause of the pain.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended adult dose is 500 mg for the first dose followed by 250 mg every six hours as needed, usually not to exceed one week of treatment. In the case of menstrual cramps, treatment is usually not necessary for longer than two or three days. Where possible, the lowest effective dose of mefenamic acid for the shortest possible period of time should be used.

It is best to take mefenamic acid with or after food.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones given here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not take this medication if you:

• are allergic to mefenamic acid or any ingredients of the medication
• are breast-feeding
• are in the third trimester of pregnancy (after 28 weeks of pregnancy)
• are less than 18 years old
• have active stomach bleeding such as gastric or duodenal ulcers
• have a history of asthma, itchy skin rash, or allergic reactions after taking ASA (acetylsalicylic acid) or other nonsteroidal anti-inflammatory drugs (NSAIDs; e.g., ibuprofen, celecoxib, diclofenac, indomethacin, etc.)
• have bleeding in the brain
• have or recently had an inflammatory condition of the stomach and intestines such as ulcerative colitis
• have recently had heart bypass surgery
• have severe or active kidney disease
• have severe or active liver disease
• have severe, uncontrolled heart failure
• have too much potassium in the body (hyperkalemia)

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• abdominal pain
• decreased or loss of appetite
• diarrhea
• dizziness
• drowsiness
• fatigue
• general feeling of being unwell
• heartburn
• lightheadedness
• nausea
• vomiting

Although most of the side effects listed below don’t happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• blurred vision or any change in vision
• changes in hearing
• persistent vomiting, heartburn, nausea, diarrhea, or stomach pain
• ringing or buzzing in the ears
• signs of allergic reaction (e.g., rash, itching or hives)
• signs of anemia (e.g., unusual tiredness or weakness, pale skin, fast heartbeat)
• signs of bleeding (e.g., unusual bleeding or bruising, bleeding gums, unexplained nosebleeds)
• signs of depression, e.g.:
• changes in sleep
• changes in weight
• decreased interest in activities
• poor concentration
• thoughts of suicide
• signs of infection, e.g.:
• fever or chills
• headache
• listlessness
• prolonged dizziness
• severe diarrhea
• shortness of breath
• stiff neck
• weight loss
• signs of liver problems, e.g.:
• dark urine
• diarrhea
• loss of appetite
• nausea
• pale stools
• vomiting
• weight loss
• yellowing of the skin or whites of the eyes
• signs of severe acid reflux (heartburn; e.g., burning feeling in the throat, chest, or stomach; difficulty swallowing; cough or hoarseness)
• signs of urinary tract problems, e.g.:
• bladder pain
• bloody or cloudy urine
• difficult, burning, or painful urination
• change in urine colour or odour
• frequent urge to urinate
• sudden, large increase or decrease in the amount of urine
• loss of bladder control

Stop taking this medication and seek immediate medical attention if any of the following side effects occur:

• signs of bleeding in the stomach, e.g.:
• bloody, black, or tarry stools
• spitting up of blood
• vomiting blood or material that looks like coffee grounds
• signs of breathing problems, e.g.:
• shortness of breath
• troubled breathing
• wheezing, or tightness in chest
• fast or irregular breathing
• signs of heart problems (e.g., fast, irregular heartbeat or pulse, chest pain, difficulty breathing, swelling of the lower legs, feet)
• signs of meningitis not caused by infection (e.g., headache [severe], throbbing, or with stiff neck or back)
• signs of a serious allergic reaction, e.g.:
• abdominal cramps
• difficulty breathing
• nausea and vomiting
• swelling of the face and throat
• signs of a severe skin reaction, e.g.:
• a rash combined with fever or discomfort
• a rash covering a large area of the body
• a rash that spreads quickly
• blistering
• peeling

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin taking a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take this medication.

Allergy: Some people who are allergic to other NSAIDs or ASA also experience allergic reactions to mefenamic acid. Before you take mefenamic acid, inform your doctor about any previous adverse reactions you have had to medications, especially NSAIDs. People who have experienced difficulty breathing after taking ASA or other NSAIDs should not take mefenamic acid.

Contact your doctor at once if you experience signs of an allergic reaction, such as skin rash, itching, difficulty breathing, or swelling of the face and throat.

Anemia: This medication may cause anemia (low red blood cells). If you take this medication for a long period of time, your doctor will periodically monitor your red blood cell levels. If you experience symptoms of anemia (e.g., shortness of breath, fatigue, pallor, fast heartbeat), contact your doctor as soon as possible.

Aseptic meningitis: Rarely, anti-inflammatory medications have been linked to symptoms of aseptic meningitis (inflammation or swelling of the membranes around the brain and spinal cord that is not caused by bacteria). If you have an autoimmune condition (e.g., systemic lupus erythematosus, mixed connective tissue disease), you are more at risk for developing this. If you experience symptoms such as stiff neck, severe headache, nausea, vomiting, fever, or changes in consciousness, stop taking this medication and get immediate medical attention.

Asthma: People with asthma are at increased risk of severe and even fatal allergic reactions (anaphylaxis) when taking this medication. If you have asthma or other breathing disorders, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Bleeding disorders: Mefenamic acid may increase bruising and bleeding from cuts may take longer to stop. If you have bleeding disorders, a history of bleeding problems, or are taking medications to prevent clotting, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Blood pressure: Mefenamic acid may cause an increase in blood pressure, even when there have been no blood pressure problems in the past. People with high blood pressure should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication and whether any special monitoring is needed. Report any ongoing increase in blood pressure to your doctor as soon as possible.

Diarrhea: If diarrhea occurs, the dosage should be reduced or the medication stopped temporarily. Certain people who develop diarrhea may be unable to tolerate the medication in the future as well.

Drowsiness/reduced alertness: Mefenamic acid may cause drowsiness or dizziness, affecting your ability to drive or operate machinery. Avoid driving, operating machinery, or performing other potentially hazardous tasks until you have determined how you are affected by this medication.

Fertility: This medication may reduce your ability to become pregnant. Taking this medication while trying to become pregnant is not recommended.

Fluid retention: Mefenamic acid can cause fluid retention and may result in swelling or puffiness. In severe cases, this can make symptoms of congestive heart failure worse. If you have congestive heart failure, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication and whether any special monitoring is needed.

Report any fluid retention, swelling or puffiness in the legs, feet, or hands, or any difficulty breathing to your doctor as soon as possible.

Heart problems: Mefenamic acid, like other NSAIDs, may increase the risk of serious heart problems such as heart attack, stroke, or blood clots. If you are at risk for heart disease, such as high blood pressure, high cholesterol, diabetes, or pre-existing heart disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication and whether any special monitoring is needed.

Kidney function: Long-term use of mefenamic acid may lead to a higher risk of reduced kidney function. This is most common for people who already have kidney disease, liver disease, or heart failure; for people who take diuretics (water pills); and seniors.

If you have kidney disease or reduced kidney function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: If you have liver disease or reduced liver function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Stomach problems: Stomach ulcers, perforation, and bleeding from the stomach have been known to occur during therapy with mefenamic acid. These complications can occur at any time, and are sometimes severe enough to require immediate medical attention. The risk of ulcers and bleeding increases when higher doses of NSAIDs are taken for longer periods of time. Mefenamic acid may prolong stomach bleeding caused by ASA. However, mefenamic acid itself appears to be less likely than ASA to cause stomach bleeding.

People who easily experience irritation of the stomach and intestines, have had a stomach ulcer in the past or have another inflammatory disease of the stomach such as ulcerative colitis or Crohn’s disease, should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication and whether any special monitoring is needed.

Stop taking the medication and contact your doctor immediately if you experience symptoms or signs that suggest stomach ulcers or bleeding in the stomach (black, tarry stools). These reactions can occur at any time during treatment without warning.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

The use of mefenamic acid during the last 3 months of pregnancy may result in harm to the baby or longer labour for the parent. Mefenamic acid should not be used during this time.

Breast-feeding: This medication passes into breast milk. If you are breast-feeding and taking mefenamic acid, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: Mefenamic acid is not recommended for children under 18 years old. The safety and effectiveness of using this medication have not been established for children.

Seniors: Seniors appear to have a higher risk of side effects, such as bleeding and kidney problems. The lowest effective dosage should be used for the shortest period of time possible.

There may be an interaction between mefenamic acid and any of the following:

• abrocitinib
• aminolevulinic acid
• ASA
• alcohol
• aliskiren
• amikacin
• aminosalicylate drugs (e.g., mesalamine, olsalazine, sulfasalazine)
• anagrelide
• angiotensin converting enzyme (ACE) inhibitors (e.g., ramipril)
• angiotensin receptor blockers (ARBs; e.g., candesartan, irbesartan, losartan)
• apixaban
• beta-adrenergic blockers (e.g., metoprolol, atenolol)
• bimatoprost
• bismuth subsalicylate
• bisphosphonates (e.g., alendronate, risedronate)
• cholestyramine
• clopidogrel
• colesevelam
• colestipol
• corticosteroids (e.g., dexamethasone, hydrocortisone, prednisone)
• cyclosporine
• dabigatran
• deferasirox
• desmopressin
• digoxin
• diuretics (water pills; e.g., furosemide, hydrochlorothiazide, spironolactone, triamterene)
• edoxaban
• eplerenone
• fondaparinux
• heparin
• herbal products that affect blood clotting (e.g., cat's claw, chamomile, fenugreek, evening primrose, feverfew, garlic, ginger, ginseng, turmeric)
• hydralazine
• latanoprost
• latanoprostene
• levothyroxine
• lithium
• low-molecular-weight heparins (e.g., dalteparin, enoxaparin, tinzaparin)
• methotrexate
• multivitamin/mineral supplements
• obinutuzumab
• omega-3 fatty acids
• other non-steroidal anti-inflammatory drugs (NSAIDs; e.g., celecoxib, ibuprofen, ketorolac, naproxen)
• pentoxifylline
• polyethylene glycol
• prasugrel
• protein kinase inhibitors (e.g., dasatinib, ibrutinib)
• quinolone antibiotics (e.g., ciprofloxacin, norfloxacin, ofloxacin)
• rivaroxaban
• selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, fluoxetine, paroxetine, sertraline)
• serotonin/norepinephrine reuptake inhibitors (SNRIs; e.g., desvenlafaxine, duloxetine, venlafaxine)
• sodium phosphates
• spironolactone
• tacrolimus
• tenofovir
• ticagrelor
• tipranavir
• travoprost
• tricyclic antidepressants (e.g., amitriptyline, clomipramine, desipramine, trimipramine)
• vancomycin
• vilazodone
• vitamin E
• warfarin

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.