This medicine can increase your risk of life-threatening heart or circulation problems, including heart attack or stroke. Do not use this medicine just before or after having heart bypass surgery (also called coronary artery bypass graft, or CABG).

Seek emergency medical help if you have symptoms of heart or circulation problems, such as chest pain, weakness, shortness of breath, slurred speech, or problems with vision or balance.

This medicine can also increase your risk of serious effects on the stomach or intestines, including bleeding or perforation (forming of a hole). These conditions can be fatal and gastrointestinal effects can occur without warning at any time while you are taking mefenamic acid. Older adults may have an even greater risk of these serious gastrointestinal side effects.

Call your doctor at once if you have symptoms of bleeding in your stomach or intestines. This includes black, bloody, or tarry stools, or coughing up blood or vomit that looks like coffee grounds.

Do not use any other over-the-counter cold, allergy, or pain medication without first asking your doctor or pharmacist.

Do not drink alcohol while taking mefenamic acid. Alcohol can increase the risk of stomach bleeding.

Important safety information: 

Tell your doctor if you are taking an antidepressant such as citalopram (Celexa), duloxetine (Cymbalta), escitalopram (Lexapro), fluoxetine (Prozac, Sarafem, Symbyax), fluvoxamine (Luvox), paroxetine (Paxil), sertraline (Zoloft), or venlafaxine (Effexor). Taking any of these drugs with mefenamic acid may cause you to bruise or bleed easily.

Before taking mefenamic acid, tell your doctor if you are taking any of the following drugs:

a blood thinner such as warfarin (Coumadin);

a diuretic (water pill) such as furosemide (Lasix);

cyclosporine (Gengraf, Neoral, Sandimmune);

lithium (Eskalith, Lithobid);

methotrexate (Rheumatrex, Trexall);

steroids (prednisone and others); or

aspirin or NSAIDs (non-steroidal anti-inflammatory drugs) such as diclofenac (Voltaren), etodolac (Lodine), fenoprofen (Nalfon), flurbiprofen (Ansaid), ibuprofen (Advil, Motrin), indomethacin (Indocin), ketoprofen (Orudis), ketorolac (Toradol), meclofenamate (Meclomen), meloxicam (Mobic), nabumetone (Relafen), naproxen (Aleve, Naprosyn), piroxicam (Feldene), and others.

This list is not complete and there may be other drugs that can interact with mefenamic acid. Tell your doctor about all the prescription and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor.

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Stop taking mefenamic acid and seek medical attention or call your doctor at once if you have any of these serious side effects:

chest pain, weakness, shortness of breath, slurred speech, problems with vision or balance;

black, bloody, or tarry stools, coughing up blood or vomit that looks like coffee grounds;

urinating less than usual or not at all;

pain, burning, or bleeding when you urinate;

nausea, stomach pain, low fever, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes);

fever, sore throat, and headache with a severe blistering, peeling, and red skin rash; or

bruising, severe tingling, numbness, pain, muscle weakness.

Less serious side effects may include:

upset stomach, mild heartburn or stomach pain, diarrhea, constipation; bloating, gas;

dizziness, headache, nervousness;

skin itching or rash;

dry mouth;

increased sweating, runny nose;

blurred vision; or

ringing in your ears.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.