Mefenamic acid is a prescription nonsteroidal anti-inflammatory drug (NSAID) used primarily for menstrual cramps and short-term pain relief. Sold under the brand name Ponstel, it belongs to a subclass of NSAIDs called fenamates, which work slightly differently from more familiar options like ibuprofen or naproxen. It’s only approved for short-term use, typically no longer than one week for general pain and two to three days for period pain.
How Mefenamic Acid Works
Like other NSAIDs, mefenamic acid blocks two enzymes (COX-1 and COX-2) that your body uses to produce prostaglandins. Prostaglandins are chemicals that sensitize your nerve endings to pain and drive inflammation. By reducing prostaglandin levels in your tissues, mefenamic acid lowers both pain and swelling at the source.
What sets mefenamic acid apart from ibuprofen or naproxen is that fenamates also appear to block the action of prostaglandins that have already been produced, not just the production of new ones. This dual mechanism is one reason the drug has a strong track record for menstrual pain specifically. One review found an 87% rate of “excellent” pain relief with fenamates, compared to 56% for ibuprofen and 56% for naproxen. That said, no head-to-head clinical trial has definitively crowned one NSAID the best option for period cramps.
What It’s Prescribed For
Mefenamic acid has two main uses:
- Primary dysmenorrhea (menstrual cramps). It’s started at the onset of bleeding and symptoms and taken for two to three days.
- Mild to moderate pain. This includes headaches, dental pain, muscle aches, and post-surgical discomfort. Treatment is limited to one week.
Because prostaglandins play a central role in both uterine cramping and the heavy bleeding that sometimes accompanies periods, mefenamic acid can address both symptoms at once. This makes it a common choice when menstrual pain is the primary complaint.
Typical Dosing
The standard approach for adults and adolescents 14 and older is a 500 mg loading dose, followed by 250 mg every six hours as needed. For menstrual cramps, you start taking it when your period begins and continue for two to three days. For other types of acute pain, the same dosing schedule applies but should not exceed one week. Taking it with food can help reduce stomach irritation.
Common Side Effects
The most frequently reported side effects are digestive. Diarrhea is especially common with mefenamic acid, more so than with many other NSAIDs. Other typical side effects include:
- Constipation, gas, or bloating
- Headache
- Dizziness
- Nervousness
- Ringing in the ears
These are generally mild and resolve once you stop taking the drug. More serious but less common reactions include signs of liver problems (nausea, loss of appetite, dark urine, yellowing of the skin or eyes) and gastrointestinal bleeding, which is a risk shared by all NSAIDs. If diarrhea becomes severe or persistent, that’s a signal to stop taking it.
Who Should Not Take It
Mefenamic acid is not safe for everyone. You should avoid it if you have:
- Aspirin-sensitive asthma or allergies. People who have had hives, asthma attacks, or severe allergic reactions after taking aspirin or another NSAID can experience the same or worse reactions with mefenamic acid.
- Kidney disease. The drug should not be used in anyone with pre-existing kidney problems or significantly reduced kidney function.
- A history of allergic reactions to the drug itself. This includes prior anaphylaxis or serious skin reactions.
- Recent heart bypass surgery. All NSAIDs carry a cardiovascular risk, and use around coronary artery bypass graft surgery is specifically contraindicated.
Pregnancy and Nursing
Mefenamic acid should not be used after about 30 weeks of pregnancy. At that stage, NSAIDs increase the risk of premature closure of a blood vessel in the fetal heart called the ductus arteriosus, which needs to stay open until birth. Trace amounts of the drug can also pass into breast milk, so nursing mothers need to weigh the risks with their provider.
Drug Interactions to Know About
Several common medications interact with mefenamic acid in ways that matter practically.
Blood thinners. Taking mefenamic acid alongside anticoagulants like warfarin significantly raises the risk of serious bleeding. The same caution applies if you take aspirin regularly, or if you’re on certain antidepressants (SSRIs or SNRIs), which also affect clotting.
Blood pressure medications. NSAIDs can blunt the effectiveness of ACE inhibitors, ARBs, and beta-blockers, meaning your blood pressure may not be as well controlled. In older adults or anyone who is dehydrated or has reduced kidney function, combining these drugs can also worsen kidney health.
Diuretics. Mefenamic acid can reduce how well loop and thiazide diuretics work, both for removing excess fluid and for lowering blood pressure. This happens because the drug interferes with the kidney’s prostaglandin-driven processes that help diuretics do their job.
How It Compares to Other Pain Relievers
For general aches and pains, mefenamic acid doesn’t offer a clear advantage over cheaper, more accessible NSAIDs like ibuprofen or naproxen. Its short maximum treatment duration and prescription-only status make it less convenient for everyday pain management.
Where it stands out is menstrual pain. The fenamate class has consistently shown higher rates of excellent pain relief for dysmenorrhea compared to ibuprofen and naproxen in clinical reviews. If over-the-counter NSAIDs aren’t controlling your cramps well enough, mefenamic acid is a reasonable next step to discuss with your provider. Its ability to reduce both the pain and the volume of menstrual bleeding gives it a practical edge for people dealing with heavy, painful periods.