BMA Concise Guide to Medicine & Drugs

Mefenamic Acid

Brand name Ponstan

Used in the following combined preparations None


Drug group Non-steroidal anti-inflammatory drug

Overdose danger rating Medium

Dependence rating Low

Prescription needed Yes

Available as generic Yes


Mefenamic acid, introduced in 1963, is a non-steroidal anti-inflammatory drug (NSAID). Like other NSAIDs, it relieves pain and inflammation. The drug is an effective painkiller and is used to treat headache, toothache, and menstrual pains (dysmenorrhoea), as well as to reduce excessive menstrual bleeding (menorrhagia). Mefenamic acid is also prescribed for long-term relief of pain and stiffness in rheumatoid arthritis and osteoarthritis.

The most common side effects of mefenamic acid are gastrointestinal: abdominal pain, nausea and vomiting, and indigestion. Other, more serious effects include kidney problems and blood disorders.


Your drug prescription is tailored for you. Do not alter dosage without checking with your doctor.

How taken/used Tablets, capsules, liquid.

Frequency and timing of doses 3 x daily with or after food.

Adult dosage range 1,500mg daily.

Onset of effect 1–2 hours.

Duration of action Up to 8 hours.

Diet advice None.

Storage Keep in original container at room temperature out of the reach of children.

Missed dose Take as soon as you remember. If your next dose is due within 2 hours, take a single dose now and skip the next.

Stopping the drug Can be safely stopped as soon as you no longer need it.

Exceeding the dose An occasional unintentional extra dose is unlikely to be a cause for concern. Large overdoses may cause poor coordination, muscle twitching, or seizures. Notify your doctor.


Gastrointestinal disturbances, such as indigestion and diarrhoea, are the most common side effects. If diarrhoea or a rash occur, the drug should be stopped and not used thereafter; you should talk to your doctor if you develop these side effects. Other side effects include dizziness, drowsiness, nausea, and vomiting; discuss with your doctor if these are severe or if abdominal pain occurs. If you experience wheezing, breathlessness, or black or bloodstained faeces, you should stop taking the drug and contact your doctor without delay. Long-term use of mefenamic acid also carries an increased risk of certain disorders (see Prolonged use).


General note Mefenamic acid interacts with a wide range of drugs to increase the risk of bleeding and/or peptic ulcers. These drugs include other non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin, and also oral anticoagulant drugs, such as warfarin, certain antidepressants, and corticosteroids.

Lithium, digoxin, phenytoin, and methotrexate Mefenamic acid may raise blood levels of these drugs to an undesirable extent.

Antihypertensive drugs and diuretics The beneficial effects of these drugs may be reduced by mefenamic acid.

Oral antidiabetic drugs Mefenamic acid may increase the blood-sugar-lowering effect of these drugs.

Ciprofloxacin The risk of seizures with this drug and related antibiotics may be increased by mefenamic acid.


Be sure to tell your doctor if:

· You have liver or kidney problems.

· You have had a peptic ulcer, oesophagitis, or acid indigestion.

· You have inflammatory bowel disease.

· You have asthma.

· You have high blood pressure.

· You are allergic to aspirin.

· You have any heart problems.

· You are taking other medicines.

Pregnancy Not usually prescribed. May cause defects in the unborn baby and, taken in late pregnancy, may affect the baby’s cardiovascular system. Discuss with your doctor.

Breast-feeding Not recommended. The drug passes into the breast milk. Discuss with your doctor.

Infants and children Reduced dose necessary.

Over 60 Increased likelihood of adverse effects.

Driving and hazardous work Avoid such activities until you have learned how mefenamic acid affects you because the drug can cause drowsiness and dizziness.

Alcohol Avoid. Alcohol may increase the risk of stomach irritation with mefenamic acid.

Surgery and general anaesthetics The drug may prolong bleeding. Discuss with your doctor or dentist before any surgery.


There is an increased risk of bleeding from peptic ulcers and in the bowel. Rarely, the drug may affect the liver, kidney, and blood. Blood tests may be carried out. There may also be an increased risk of heart attack and stroke. The lowest effective dose is given for the shortest duration.