Approved indications In the United States, oral mefenamic acid is approved for: (1) short-term relief of mild to moderate pain in patients 14 years and older, when treatment will not exceed 7 days; and (2) treatment of primary dysmenorrhea (menstrual cramps) using short courses during menses.

• Pain uses include headaches, dental pain, musculoskeletal pain, and postoperative pain when a short NSAID course is appropriate.
• For primary dysmenorrhea, it is started at the onset of menstrual bleeding and cramping and continued for about 2–3 days.

Common off-label uses and evidence Clinicians may use mefenamic acid off-label for heavy menstrual bleeding (menorrhagia) and other gynecologic or musculoskeletal pains when an NSAID is appropriate.

• Randomized trials show that mefenamic acid can reduce menstrual blood loss by roughly 20–40% in many women with heavy menstrual bleeding, though antifibrinolytic drugs like tranexamic acid usually reduce bleeding more.
• It is also used as an alternative NSAID when patients have responded poorly or had side effects with other NSAIDs, though overall analgesic effectiveness is similar across the class.

Efficacy expectations For pain and cramps, many people begin to notice relief within about 1 hour of a dose, with peak effect in 2–4 hours.

• With correct dosing, most patients experience meaningful reduction in pain severity; some may achieve near-complete relief, others only partial improvement.
• In primary dysmenorrhea, short courses each cycle can significantly reduce cramping pain and may modestly reduce menstrual blood loss.
• Compared with other NSAIDs (such as ibuprofen or naproxen), mefenamic acid provides similar short-term pain relief; it is not clearly more effective overall, but may be preferred by some individuals based on personal response.

Typical dosing (oral capsules)

• Acute mild to moderate pain (age ≥14 years): 500 mg by mouth once, then 250 mg every 6 hours as needed, usually for no longer than 7 days.
• Primary dysmenorrhea (menstrual cramps, age ≥14 years): 500 mg once at onset of bleeding and pain, then 250 mg every 6 hours, typically for 2–3 days each cycle.
• Always use the lowest effective dose for the shortest possible time.

How to take it

• Swallow capsules with a full glass of water, preferably with food, milk, or an antacid to lessen stomach upset.
• Avoid taking other prescription or over‑the‑counter NSAIDs (e.g., ibuprofen, naproxen, aspirin at pain‑relief doses) at the same time unless specifically directed.
• Limit or avoid alcohol, which increases the risk of stomach bleeding.

Special dosing considerations

• Not recommended for children under 14 years due to insufficient safety data.
• Use cautiously and often at reduced doses or with close monitoring in older adults and in people with mild kidney, liver, heart, or gastrointestinal disease, or those taking interacting medications.
• Do not use for chronic daily therapy; it is intended for short, intermittent courses.

Missed dose

• If you are on a scheduled regimen and miss a dose, take it as soon as you remember unless it is almost time for the next dose.
• If it is near the time for your next dose, skip the missed dose and resume your regular schedule; do not double doses.

Overdose

• Symptoms can include severe stomach pain, vomiting, drowsiness, confusion, seizures, difficulty breathing, or signs of kidney failure.
• In case of suspected overdose, contact emergency services or a poison control center (in the U.S., 1‑800‑222‑1222) immediately; do not wait for symptoms to worsen.

Common side effects Most side effects are gastrointestinal or nervous system–related and are usually mild to moderate.

• Stomach pain, heartburn, nausea, vomiting, diarrhea, constipation, gas, or indigestion.
• Headache, dizziness, drowsiness, or a general feeling of being unwell.
• Mild skin rash or itching, fluid retention or swelling in the legs or feet, and increased blood pressure in some people.
• These effects often appear early in treatment and may improve if the drug is taken with food and used for only a few days.

Serious or rare adverse effects (seek immediate medical care)

• Signs of gastrointestinal bleeding or ulcer: black or bloody stools, vomiting blood or material that looks like coffee grounds, severe or persistent stomach pain.
• Cardiovascular events: chest pain, shortness of breath, sudden weakness on one side, trouble speaking, or sudden severe headache (possible heart attack or stroke).
• Kidney problems: decreased or dark urine, swelling in legs or face, unusual fatigue, or sudden weight gain.
• Liver injury: yellowing of the skin or eyes, dark urine, pale stools, persistent nausea, vomiting, or right‑upper‑abdominal pain.
• Severe skin reactions (Stevens–Johnson syndrome/toxic epidermal necrolysis): blistering or peeling skin, widespread rash, sores in the mouth, eyes, or genitals, or fever with rash.
• Allergic reactions and asthma exacerbations: hives, wheezing, difficulty breathing, swelling of the face, lips, tongue, or throat, especially in people with aspirin/NSAID allergy.

Warnings and precautions

• Cardiovascular risk: Like other non-aspirin NSAIDs, mefenamic acid carries a boxed warning for increased risk of heart attack and stroke, especially with higher doses, longer use, and in people with existing cardiovascular disease.
• Gastrointestinal risk: It can cause serious stomach or intestinal bleeding and ulcers, which may occur without warning; risk is higher in older adults, people with a prior ulcer or GI bleed, heavy alcohol use, or concurrent corticosteroids, anticoagulants, or other NSAIDs.
• Kidney and liver disease: Avoid in significant renal disease or advanced hepatic disease; use cautiously and usually at the lowest effective dose with monitoring in milder impairment.
• Asthma and allergies: Contraindicated in patients who have asthma, urticaria, or allergic reactions with aspirin or other NSAIDs.
• Pregnancy: NSAIDs, including mefenamic acid, should generally be avoided from 20 weeks of gestation onward unless specifically advised by a clinician, and avoided after 30 weeks because of risks such as low amniotic fluid and premature closure of the fetal ductus arteriosus.
• Breastfeeding: Small amounts enter breast milk; short-term use may be acceptable in some cases, but risks and benefits should be discussed with a clinician.
• Age limits: Safety and efficacy are not established in children under 14 years; older adults have higher GI, kidney, and cardiovascular risks and may need extra caution or alternative therapies.

Relative safety compared with other NSAIDs Mefenamic acid shares the class risks of all traditional NSAIDs (GI bleeding, kidney injury, cardiovascular events); short-term, low-dose use has a safety profile broadly similar to agents like ibuprofen or naproxen, but it is not safer for long-term use and is generally intended only for brief courses.

Reporting side effects and safety updates Patients and caregivers in the United States can report suspected side effects to the FDA MedWatch program (online or by calling 1‑800‑FDA‑1088), and can check FDA safety communications for any new warnings about NSAIDs or mefenamic acid.

Major drug and substance interactions

• Other NSAIDs and high‑dose aspirin: Increases risk of stomach bleeding and ulcers; avoid combining unless supervised.
• Anticoagulants and antiplatelets (e.g., warfarin, DOACs, heparin, clopidogrel) and some antidepressants (SSRIs/SNRIs): Higher risk of bleeding; may require closer monitoring.
• ACE inhibitors, ARBs, and diuretics: NSAIDs can reduce blood pressure–lowering effects and increase kidney risk, especially in dehydrated or older patients.
• Lithium and methotrexate: NSAIDs can raise blood levels and toxicity risk; dose adjustments and monitoring may be needed.
• Cyclosporine and tacrolimus: Increased risk of kidney toxicity when combined with mefenamic acid.
• Corticosteroids (e.g., prednisone): Additive risk of gastrointestinal bleeding or ulcer.
• Alcohol: Regular or heavy use increases GI bleeding risk when combined with NSAIDs.
• Herbal supplements that affect clotting (e.g., ginkgo, garlic, ginseng, high‑dose fish oil): May increase bleeding risk when used with mefenamic acid.

Conditions requiring extra caution or avoidance

• History of peptic ulcer disease, GI bleeding, or inflammatory bowel disease.
• Known cardiovascular disease (prior heart attack, stroke), uncontrolled hypertension, or severe heart failure.
• Chronic kidney disease or significant liver impairment.
• Asthma or prior reactions (wheezing, hives, anaphylaxis) to aspirin or other NSAIDs.
• Bleeding disorders, low platelets, or concurrent use of multiple blood‑thinning agents.
• Pregnancy, especially at or after 20 weeks, and breastfeeding without clinician guidance.

Monitoring needs

• For short-term courses in otherwise healthy people, routine lab monitoring is usually not needed.
• For repeated or higher‑risk use, clinicians may check blood pressure, kidney function (serum creatinine, BUN), liver enzymes, and sometimes blood counts, particularly in older adults or those with comorbidities.
• Patients should promptly report symptoms of GI bleeding, chest pain, breathing difficulty, marked swelling, sudden weight gain, or rash.

Q: How quickly will mefenamic acid relieve my pain or menstrual cramps?
A: Many people start to feel relief within about an hour of a dose, with maximum effect in 2–4 hours, especially when it is taken at the first sign of pain or at the onset of menstrual bleeding.

Q: How many days in a row can I safely take mefenamic acid?
A: For general pain it is usually limited to 7 days or less, and for menstrual cramps typically 2–3 days per cycle, using the lowest dose that controls your symptoms.

Q: Can I take mefenamic acid together with ibuprofen or naproxen?
A: No, you should generally avoid combining mefenamic acid with other NSAIDs like ibuprofen or naproxen because this greatly increases the risk of stomach bleeding, ulcers, and kidney problems; instead, use one NSAID as directed.

Q: Is mefenamic acid stronger or better than ibuprofen for period pain?
A: Mefenamic acid and ibuprofen are both effective NSAIDs for menstrual cramps, and most studies suggest similar overall pain relief; some individuals find one works better or causes fewer side effects, so choice often depends on personal response and clinician preference.

Q: Is mefenamic acid safe during pregnancy or while trying to conceive?
A: NSAIDs like mefenamic acid are generally avoided from 20 weeks of pregnancy onward and may be limited earlier; they can also temporarily affect ovulation, so if you are pregnant, may be pregnant, or are trying to conceive, discuss safer alternatives (such as acetaminophen when appropriate) with your clinician.

Q: What should I do if I have side effects while taking mefenamic acid?
A: Stop the medicine and seek urgent care for serious symptoms such as chest pain, trouble breathing, severe stomach pain, black stools, vomiting blood, sudden swelling, or widespread rash, and for non‑urgent side effects contact your clinician and consider reporting the event to FDA MedWatch (for example, by phone at 1‑800‑FDA‑1088).

Storage Store mefenamic acid capsules at room temperature (about 68–77°F / 20–25°C) in a tightly closed container, away from excess heat, moisture, and direct light, and out of reach of children and pets.

Keep the medicine in its original labeled container and do not use it past the expiration date.

Disposal When you no longer need the medication or it is expired, use a drug take-back program if available through your pharmacy, clinic, or community collection site.

If no take-back option is available, ask your pharmacist about safe household disposal; in general, do not flush mefenamic acid down the toilet unless specifically instructed, and mix unused capsules (out of the capsule shell) with an unappealing substance (like used coffee grounds or kitty litter) in a sealed bag before placing in household trash.