Mefenamic Acid (Ponstel) - Uses, Side Effects, and More

What are the most common side effects of mefenamic acid?

The most common side effects of mefenamic acid are listed below. Tell your health care provider if you have any of these side effects that bother you.

• Upset stomach or stomach pain
• Constipation or diarrhea
• Gas or heartburn
• Nausea and vomiting
• Dizziness
• Headache
• Skin rash or itching
• Fluid retention
• Bleeding (see below)
• Ringing in the ears

There may be other side effects of mefenamic acid that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of mefenamic acid?

While less common, the most serious side effects of mefenamic acid are described below, along with what to do if they happen.

Severe Allergic Reactions. Mefenamic acid can cause allergic reactions, including a specific type of allergic reaction called DRESS. DRESS stands for drug reaction with eosinophilia and systemic symptoms. It is also sometimes called multi-organ hypersensitivity. This is a reaction that can affect multiple parts of the body including your liver, kidneys, and heart. Stop taking the medicine and get help right away if you have any of the following symptoms of a serious allergic reaction.

• Breathing problems or wheezing
• Racing heart
• Itching or skin rash
• Bumps on the skin called hives that can be red, pink, white, or brown depending on your skin tone
• Fever or general ill feeling
• Swollen lymph nodes
• Swelling of the face, lips, mouth, tongue, or throat
• Shortness of breath, trouble swallowing, or throat tightness
• Swelling in your feet, ankles, or legs
• Nausea or vomiting
• Dizziness, feeling lightheaded, or fainting
• Stomach cramps
• Joint pain
• Dark-colored pee
• Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Heart Attack and Stroke. Mefenamic acid can increase your risk of a heart attack or stroke that can lead to death. This risk is higher in people who already have heart disease and with longer use of mefenamic acid and higher doses. Do not take mefenamic acid if you have had a recent heart attack without talking to your health care provider. This could increase your risk of having another heart attack. Get emergency help if you have any of the following symptoms of a heart attack or stroke.

• Chest pain or pressure
• Fast or abnormal heartbeat
• Trouble breathing
• Pain in your back, jaw, throat, or arm
• Sweating, upset stomach, vomiting, or dizziness
• Sudden weakness on one side of your body
• Sudden and severe headache
• Slurred speech or trouble understanding speech

Bleeding. Mefenamic acid can increase your risk of bleeding, especially if you have a bleeding disorder or take other medicines that increase your risk of bleeding. Tell your health care provider right away if you notice signs of bleeding including easy bruising or bleeding.

Stomach Bleeding. Mefenamic acid can increase your risk of bleeding, ulcers, and tears (perforation) in your gut. The risk is higher if you have a history of stomach ulcers, or bleeding problems, take higher doses of mefenamic acid or take it for longer than directed, have poor health, are age 60 or older, have liver disease, smoke, drink alcohol, or take certain other medicines. Stop taking mefenamic acid and get emergency help right away if you have any of the following symptoms.

• Vomit blood
• Black or tarry poop
• Stomach pain that does not go away
• Upset stomach
• Feel faint

Liver Damage. Liver damage, also called hepatotoxicity, can happen when taking mefenamic acid. Call your health care provider right away if you have any of the following symptoms of liver damage.

• Nausea or vomiting
• Stomach or belly pain
• Fever
• Weakness or unusual tiredness
• Itching
• Loss of appetite
• Light-colored poop
• Dark-colored urine (pee)
• Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Increased Blood Pressure (Hypertension). Mefenamic acid may increase your blood pressure or make it worse if you have a history of high blood pressure. Call your health care provider if your blood pressure increases while taking this medicine.

If you measure your blood pressure and the top number (systolic) is 180 mm Hg or higher or the bottom number (diastolic) is 120 mm Hg or higher, get medical attention right away. Increases in blood pressure may not be noticeable but look out for any of the following symptoms of severely high blood pressure.

• Sudden severe headache
• Chest pain
• Dizziness or confusion
• Trouble breathing
• Nausea/vomiting
• Blurry or other changes to vision
• Anxiety
• Buzzing in the ears
• Nosebleed
• Feeling of skipped heart beats

Heart Failure. Mefenamic acid may increase your risk of heart failure. Tell your health care provider right away if you have any of the following symptoms of heart failure.

• Shortness of breath or trouble breathing, especially while lying down
• Swelling in your feet, ankles, or legs
• Unusually fast weight gain
• Unusual tiredness

Kidney Damage. Kidney damage can happen when taking mefenamic acid. Call your health care provider right away if you have any of the following symptoms of kidney damage.

• Reduced need to pee
• Swelling in your feet, ankles, or legs
• Weakness or unusual tiredness
• A hard time catching your breath or chest pain/pressure
• Confusion
• Nausea
• Seizures

Increased Potassium Level (Hyperkalemia). Mefenamic acid can increase the potassium levels in your blood (hyperkalemia), especially if your kidneys are not working as well as they should be. Mild increases in potassium levels may not cause any symptoms. Stop taking the medicine and call your health care provider right away if you have any of the following symptoms of a high potassium level. 

• Muscle weakness or unusual tiredness
• Slow heartbeat or feeling of skipped heartbeats 
• Nausea or vomiting
• Trouble breathing
• Abnormal heart rhythm

Severe Skin Reactions. NSAIDs, including mefenamic acid, can cause rare but serious skin reactions such as exfoliative dermatitis, Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and fixed drug eruption (FDE), that can lead to death if not treated. If you get a rash or blisters, stop taking mefenamic acid and call your health care provider right away. Get emergency help if you have any of the following symptoms.

• Painful skin that looks burned or peels off
• A flat rash or areas of skin discoloration
• Blisters or sores on the skin, mouth, nose, eyes, or genitals
• Red, painful, or watery eyes
• Flu-like symptoms including fever, chills, or muscle aches
• Darkened patches or blisters that appear in the same place after taking the medicine

Anemia. Mefenamic acid may cause anemia, which is when you have low levels of red blood cells. Tell your health care provider if you have any of the following symptoms of anemia.

• Unusual weakness or tiredness
• Cold hands and feet
• Fast or abnormal heartbeat
• Pale or yellowish skin 
• Dizziness, lightheadedness, or feeling like you are about to pass out
• Shortness of breath