Guide to Mefenamic Acid Usage

Mefenamic acid is a common medication used to treat various types of pain. It belongs to a group of drugs called non-steroidal anti-inflammatory drugs (NSAIDs), which is typically taken by mouth. It works by reducing your body's production of an inflammatory substance that causes fever, swelling and pain.

Precautions Before Taking Mefenamic Acid

Although mefenamic acid is a medication that may be bought over-the-counter, there are some things to keep in mind before taking it, including:

  • Tell your doctor/pharmacist if you are allergic to mefenamic acid, aspirin or other NSAID such as ibuprofen or naproxen. It is also safe practice to inform your doctor about other allergies because medications may contain other ingredients, which may also cause allergic reactions.
  • It may not be advisable to take this medication if you have certain health conditions. Consult your doctor/pharmacist if you have: aspirin-induced asthma, severe kidney disorder, recent history of heart bypass surgery, and bleeding tendencies, including stomach ulcers or gastrointestinal bleeding.
  • Tell your doctor/pharmacist if you have a history of: asthma, high blood pressure, blood disorders such as anemia, bleeding or clotting problems, heart disease, stroke, diabetes, liver disease, nasal polyps, tobacco use, obesity, gastrointestinal problems such as recurring heartburn, swelling of the hands/ankles/feet.
  • If you have kidney problems, it is important for you to avoid dehydration while taking NSAIDs, such as mefenamic acid. Drink plenty of water/fluids according to your doctor’s advice.
  • Tell your doctor/dentist before having any surgery if you are using this drug.
  • Mefenamic acid may make you drowsy or dizzy. Avoid driving, using machinery, or doing any activity that requires you to be alert. Avoid taking alcoholic beverages while using the drug.
  • Be advised that mefenamic acid may increase your risk of stomach bleeding, especially while using alcohol or tobacco.
  • Using this medication may increase your sensitivity to the sun. Avoid prolonged exposure to the sun, sunlamps, or tanning booths. When outdoors, use sun protection such as sunscreen and protective clothing.
  • Elderly individuals are advised to use mefenamic acid with caution because they may be more sensitive to its effects. Your kidney function declines with age, which may increase your risk of side effects.
  • Women who may be pregnant must talk with their doctor before taking mefenamic acid to avoid any possible harm, especially during the first and last trimesters of pregnancy.
  • If you are breast-feeding, consult your doctor before taking mefenamic acid  since it is passed through the milk.

Take Mefenamic Acid Safely

Take mefenamic acid as directed by your doctor or as written on the medication’s label. You should check with your doctor or pharmacist if you are not sure. The following are some important things you should keep in mind when taking mefenamic acid:

  • Mefenamic acid 500 mg should be taken with food or after meals. Swallow the mefenamic acid tablets whole with water. The usual dose of mefenamic acid for adults is one tablet 3 times per day.
  • If you are taking mefenamic acid for menstrual pain during excessively heavy periods, start taking it on the first day of bleeding and continue using it as directed by your doctor.
  • Generally, the lowest effective dose of mefenamic acid should be taken. Elderly individuals may use the regular adult dose, but it should be used with care in dehydrated patients or those who have kidney disease. And mefenamic acid 500 mg is not recommended for use in children.
  • If you have stomach ulcers or other gastrointestinal problems, inform your doctor/pharmacist if you experience unusual symptoms such as blood in your stool.
  • Watch out for some side effects. Taking more than 500 mg mefenamic acid may cause nausea, vomiting, headache, abdominal pain, bloody stool or vomit, diarrhea,ringing in ear, disorientation, drowsiness, excitation, dizziness, fainting, convulsions, and coma. Acute poisoning may lead to liver damage and acute kidney failure. Call your doctor or go to your local hospital immediately, and don’t forget to bring the remaining tablets with the container with you.
  • If you forget to take your dose, take the next dose when it is due and continue following your usual schedule. Avoid taking a double dose. Ask your doctor/pharmacist if you have other concerns.

Possible Side Effects and Interactions with Mefenamic Acid

Mefenamic is effective in treating pain and inflammation, but like other medications, it may have some side effects. It may also interact with other medications or medical conditions, so it’s advisable to tell your doctor if you are taking other medications. Let’s take a look at the side effects and interactions when taking mefenamic acid.

Side Effects


  • Chest pain, shortness of breath, weakness, slurred speech, vision/balanceproblems
  • Coughing up blood, bloody, black/tarry stools, coffee ground appearance of vomit
  • Decreased urination
  • Painful or bloody urine
  • Loss of appetite, stomach pain, nausea, low fever, clay-colored stools, dark urine, yellowing of the skin/eyes
  • Sore throat, fever and headache with skin rash
  • Bruising, numbness, severe tingling, muscle weakness,  pain
  • Upset stomach, stomach pain, constipation/diarrhea, bloating, gas
  • Headache, dizziness, nervousness
  • Rash, skin itching
  • Dry mouth
  • Runny nose, increased sweating
  • Ringing in the ears
  • Blurred vision
  • Very serious interactions with cidofovir and ketorolac
  • Medications containing pain relievers or fever reducers such as aspirin and NSAIDs such as ibuprofen and celecoxib
  • An increased risk of bleeding when taken with anti-platelet drugs (ex. Clopidogrel) and "blood thinners" (ex. enoxaparin, Dabigatran, warfarin)
  • Let your doctor know the following medications that you are taking before using mefenamic acid: nonprescription or herbal products such as aliskiren, angiotensin II receptor blockers (ex. valsartan, losartan), ACE inhibitors (ex.  captopril, lisinopril), "water pills" (diuretics such as furosemide), cyclosporine, desmopressin, corticosteroids (ex.  prednisone), fluconazole, lithium, pemetrexed, probenecid, methotrexate, tenofovir 

What to Do in Case of an Emergency

When Experiencing Serious Symptoms

Stop using mefenamic acid and immediately contact your doctor IF:

  • You experience breathing problems, such as breathlessness or wheezing.
  • You have any symptoms of allergic reaction, such as skin rash or swelling of the faceoraround your mouth.
  • You have severe diarrhea, black or bloody stools, blood in your vomit, or abdominal pains.
  • You experience other symptoms which may be due to mefenamic acid.

When Overdosing

Call your local poison control center immediately. If a victim has collapsed or is not breathing, call 911 right away.

As mentioned above, mefenamic acid overdose symptoms include:

  • Nausea
  • Vomiting
  • Extreme tiredness
  • Stomach pain
  • Blood in vomit
  • Vomit looks like ground coffee
  • Bloody or black, tarry stools
  • Slowed breathing
  • Loss of consciousness