What Is Mefenamic Acid Used For and How Does It Work?

Mefenamic acid is a non-steroidal anti-inflammatory drug (NSAID) that has been used since the 1960s, primarily to treat period pain and heavy menstrual bleeding. It belongs to a chemical family called fenamates, which gives it a few unusual properties that set it apart from more familiar painkillers like ibuprofen or naproxen. Despite being widely prescribed in parts of Asia, the UK, and elsewhere, it remains relatively obscure in the United States, where ibuprofen and naproxen dominate the over-the-counter painkiller shelf. That lower profile belies a surprisingly complex pharmacological profile, with research interest expanding well beyond menstrual pain.

How It Works

Like all NSAIDs, mefenamic acid reduces pain and inflammation by blocking cyclooxygenase (COX) enzymes, which produce prostaglandins. Prostaglandins are chemicals your body makes at sites of injury or inflammation; they also trigger the uterine contractions that cause menstrual cramps. By suppressing prostaglandin production, mefenamic acid eases both pain and the cramping itself.

What makes mefenamic acid interesting at the molecular level is that it doesn’t interact with COX enzymes in quite the same way as ibuprofen. Research on its binding to COX-2 has shown that some NSAIDs, including mefenamic acid, act in a “substrate-selective” way: they are relatively weak at blocking the processing of one fatty acid (arachidonic acid) but potent at blocking the processing of endocannabinoids by the same enzyme.¹ This selectivity may partly explain why fenamates have effects that don’t line up neatly with what you’d expect from a generic COX inhibitor.

Activity Beyond Pain Relief

One of the more unusual findings about mefenamic acid is that it interacts with GABA receptors in the brain. GABA is the main inhibitory neurotransmitter, essentially the brain’s “calm down” signal. Lab studies have shown that mefenamic acid can boost the effect of GABA at certain receptor types, making the receptor more responsive to lower concentrations of GABA. At higher concentrations, mefenamic acid can even activate these receptors directly, without GABA being present at all.²

This effect is selective. It depends on which subunit combinations make up the GABA receptor. Mefenamic acid potentiates receptors containing certain subunit combinations but actually inhibits others.³ This dual action on brain receptors helps explain a clinical paradox: at therapeutic doses the drug can have a mild sedating or anti-seizure quality, but in overdose it can trigger convulsions. The balance tips depending on which receptor populations are being affected at a given concentration.

Period Pain and Heavy Bleeding

The condition mefenamic acid is most commonly prescribed for is primary dysmenorrhea, or painful periods not caused by an underlying pelvic condition. In a classic placebo-controlled trial, mefenamic acid produced complete relief of all dysmenorrhea symptoms in about 89% of patients across treated cycles, compared to only 13% who experienced even moderate relief on placebo.⁴ Other early controlled studies confirmed that treatment led to significant decreases in the frequency and severity of symptoms and reduced the need for additional painkillers.⁵

This effectiveness isn’t just about painkilling. Because prostaglandins drive both the pain and the excessive uterine contractions of dysmenorrhea, blocking them at the source tackles the problem more directly than a simple analgesic would. That is also why mefenamic acid has a second gynecological use: reducing heavy menstrual bleeding (menorrhagia). In women with unexplained heavy periods, mefenamic acid treatment cut median menstrual blood loss roughly in half, from about 137 ml per cycle down to about 76 ml, though the reduction varied widely between individuals.⁶ The practical appeal is that you take it only during the days you’re actually bleeding, making it a short-course option compared to hormonal treatments.

How It Stacks Up Against Other Painkillers for Period Pain

If mefenamic acid works well for cramps, a fair question is whether it works any better or worse than the ibuprofen already sitting in your medicine cabinet. A large network meta-analysis that pooled data from many randomized trials found that mefenamic acid’s pain-relief efficacy for dysmenorrhea was broadly similar to that of ibuprofen, naproxen, diclofenac, and several other NSAIDs. All of these were significantly more effective than aspirin. But the analysis did highlight a distinction on the safety side: mefenamic acid and tiaprofenic acid were flagged as the safest of the NSAIDs studied for this indication, while indomethacin carried the highest risk of adverse effects.⁷

A randomized trial comparing mefenamic acid, ginger extract, and ibuprofen found no significant differences among the three for pain severity, pain relief, or patient satisfaction.⁸ Another trial comparing mefenamic acid to ginger alone confirmed that both significantly reduced pain over time, with no meaningful difference between them.⁹ So the bottom line for dysmenorrhea is that mefenamic acid is effective but not dramatically superior to other NSAIDs. Its niche rests more on its favorable short-course safety profile and its dual ability to reduce both pain and bleeding volume.

Use in Children With Fever

In several countries, particularly in South and Southeast Asia, mefenamic acid is commonly used as a fever reducer in children. A randomized controlled trial comparing mefenamic acid (at 6 mg per kg) to standard-dose and high-dose paracetamol in febrile children found that mefenamic acid lowered temperature by about 0.45°C over 60 minutes, essentially matching the performance of high-dose paracetamol and outperforming the standard dose.¹⁰ Mefenamic acid also appeared to keep fever from returning for longer, with the time to the next fever spike averaging close to 9 hours compared to about 5 hours for standard-dose paracetamol. Adverse effects like vomiting and appetite loss did not differ significantly among the groups.

An Indian pediatric consensus statement noted that mefenamic acid shows superior antipyretic efficacy compared to paracetamol and ibuprofen in some data, with preclinical evidence hinting at possible antiviral activity and a role in managing febrile seizures. However, the same consensus acknowledged that long-term safety data in children remain limited, and further research is needed.¹¹ In countries where mefenamic acid is not routinely used in children, clinicians tend to stick with paracetamol and ibuprofen as first-line fever treatments, largely because their long-term pediatric safety profiles are more thoroughly documented.

Gastrointestinal Side Effects

Like all NSAIDs, mefenamic acid can cause stomach upset, nausea, and diarrhea. Most people tolerate short courses without problems, but prolonged use introduces a more concerning risk. Case reports and literature reviews have described severe small-bowel enteropathy in patients taking mefenamic acid over long periods. These patients developed chronic diarrhea and significant weight loss. Biopsies showed flattened intestinal villi and inflammatory infiltration, findings that can mimic celiac disease closely enough to cause misdiagnosis.¹² Symptoms resolved after stopping the drug, which is the key diagnostic clue. This complication is rare and tied to long-term use, but it underscores why mefenamic acid prescriptions typically specify short courses, often no more than seven days at a stretch.

Kidney Risks

Mefenamic acid shares the NSAID class effect of potentially harming the kidneys, but some evidence suggests it carries a specific pattern of renal injury worth knowing about. A series of clinical cases described acute kidney failure in patients on mefenamic acid, with biopsies showing inflammation both in the kidney’s filtering structures and in the tissue between them. Most patients were not producing abnormally low amounts of urine, and many had signs of salt and water depletion from accompanying diarrhea and vomiting. All recovered after stopping the drug, though some had mild residual kidney impairment.¹³

An important wrinkle is that this kidney damage does not appear to be strictly dose-dependent for interstitial injury. Prolonged use and excessive doses both increase risk, but some individuals develop the problem at standard doses.¹⁴ Animal models have confirmed that chronic dosing produces dose-dependent kidney damage including glomerular necrosis and tubular atrophy, with corresponding rises in blood markers of kidney function.¹⁵ For the typical user taking a few days’ course for period pain, kidney risk is very low. It becomes a meaningful concern for anyone taking it regularly, especially older adults or people with pre-existing kidney problems.

Overdose and Seizures

This is where mefenamic acid distinguishes itself from other NSAIDs in a genuinely dangerous way. In overdose, mefenamic acid causes seizures at a rate that dwarfs other NSAIDs. An analysis of cases reported to the UK National Poisons Information Service found that people who overdosed on mefenamic acid were roughly eight times more likely to experience central nervous system toxicity than those who overdosed on other NSAIDs. For convulsions specifically, the risk was about 82 times higher.¹⁶ This effect was dose-related and also influenced by age.

A recent case report illustrated the pattern. A young woman who intentionally ingested 2.5 grams of mefenamic acid (about 60 mg per kg body weight) developed generalized seizures within three hours. Her serum drug level was well above the toxic threshold, and she also developed acute kidney injury.¹⁷ The seizure risk in overdose likely relates to the GABA receptor interactions described earlier. At very high concentrations, the drug’s inhibitory effects on certain GABA receptor subtypes may overwhelm its potentiating effects on others, tipping the brain toward excitation rather than calm. This makes mefenamic acid a drug that deserves careful storage and awareness, particularly in households where intentional overdose is a risk.

Cardiovascular Considerations

All NSAIDs carry some cardiovascular concern, particularly for people with high blood pressure or existing heart disease. A population-based study comparing different NSAIDs in patients with hypertension found that COX-2-selective NSAIDs (like celecoxib and its relatives) carried about double the cardiovascular risk compared to mefenamic acid.¹⁸ This positions mefenamic acid favorably within the NSAID class for cardiovascular safety, though any NSAID should still be used cautiously and briefly in people with heart conditions.

Interactions With Other Drugs

One clinically significant interaction that has been documented involves lithium, a mood stabilizer used for bipolar disorder. A case report described an elderly patient stabilized on lithium who developed acute lithium toxicity shortly after starting mefenamic acid. The likely mechanism is that mefenamic acid, by inhibiting prostaglandins in the kidney, reduced the kidney’s ability to excrete lithium, causing levels to rise into the toxic range.¹⁹ This interaction is not unique to mefenamic acid, as other NSAIDs can raise lithium levels too, but the case highlights the need for caution when combining the two, particularly in older patients or those with compromised kidney function. The broader point applies to anticoagulants, other blood-pressure-lowering drugs, and methotrexate, all of which can interact with NSAIDs generally.

Research on Brain Inflammation and Alzheimer’s Disease

Some of the most intriguing recent research on mefenamic acid has nothing to do with period pain. It centers on the NLRP3 inflammasome, a protein complex inside immune cells that, when activated, triggers a cascade of inflammation. Overactivation of this complex in the brain is increasingly linked to neurodegenerative diseases. A 2016 study published in Nature Communications found that fenamate NSAIDs, including mefenamic acid, inhibit the NLRP3 inflammasome. In rodent models of Alzheimer’s disease, mefenamic acid prevented memory deficits caused by amyloid-beta injections. Treated mice showed levels of brain inflammation and microglial activation reduced to those of healthy mice.²⁰ The protective effect persisted for weeks after treatment ended.

More recent animal work has extended this finding to sepsis-related brain damage. Rats treated chronically with mefenamic acid after sepsis showed reduced neuroinflammation, better mitochondrial function, and lower accumulation of amyloid-beta in the brain, along with preserved cognitive function.²¹ These are rodent studies, not human trials, and the history of Alzheimer’s research is littered with treatments that worked beautifully in mice and failed in people. Still, the NLRP3 pathway is a real and active target in neuroinflammation research, and the fact that a cheap, already-approved drug can hit it has generated genuine interest. Clinical trials would need to weigh the drug’s known risks, especially kidney and GI effects with long-term use, against any potential neuroprotective benefit.

Why It Exists in Multiple Crystal Forms

A quirk of mefenamic acid’s chemistry that matters more than you might expect is that it can crystallize into at least two different solid forms, known as polymorphs. Form II dissolves faster and reaches higher concentrations in solution than Form I across a range of solvent systems.²² Since a drug needs to dissolve before your body can absorb it, which crystal form ends up in a tablet can affect how quickly and completely the drug gets into your bloodstream. This is why pharmaceutical manufacturers have to carefully control crystallization during production. A generic tablet made carelessly could contain a different polymorph ratio than the branded version, potentially altering its performance even though the chemical formula on the label is identical.

Environmental Persistence

Mefenamic acid turns up in places you wouldn’t want a drug to be. A study of Swiss sewage treatment plants found that at most half of the mefenamic acid entering wastewater was removed during treatment, leaving concentrations in effluent in the range of 150 to 2,000 nanograms per liter. An environmental risk assessment concluded that mefenamic acid poses a potential risk to aquatic ecosystems, with predicted environmental concentrations exceeding predicted no-effect concentrations.²³ This is not unique to mefenamic acid; ibuprofen and diclofenac showed similar persistence. But it adds to the growing evidence that pharmaceutical pollution in waterways is a genuine ecological concern, not just a theoretical one. In countries where mefenamic acid is heavily prescribed, its environmental footprint may be proportionally larger.