Naproxen is one of the most effective over-the-counter options for menstrual cramps. It works by cutting the production of the chemicals that make your uterus contract painfully, and a single dose can provide relief for up to 12 hours, which is roughly twice as long as ibuprofen lasts. In pooled clinical data, both the 200 mg and 400 mg doses outperformed placebo and acetaminophen (Tylenol) for period pain relief.
Why Naproxen Works for Cramps
Menstrual cramps happen because your uterine lining releases hormone-like chemicals called prostaglandins. These trigger the muscle contractions that shed the lining each month, and higher prostaglandin levels mean stronger, more painful contractions. Naproxen blocks the enzymes responsible for making prostaglandins, which directly reduces both the intensity and frequency of those contractions.
The effect is measurable. In a study of women with painful periods, naproxen sodium reduced one key prostaglandin in menstrual blood from an average of 227 ng/ml down to 42 ng/ml, roughly an 80% drop. A second prostaglandin fell by about 70%. That decrease in uterine prostaglandins corresponded with lower intrauterine pressure and meaningful pain relief.
How It Compares to Ibuprofen and Acetaminophen
A pooled analysis of five clinical trials compared naproxen head-to-head with ibuprofen, acetaminophen, and placebo. Naproxen at 400 mg kicked in faster than acetaminophen, providing greater relief within 30 minutes. By the six-hour mark, both the 400 mg and 200 mg naproxen doses outperformed ibuprofen and acetaminophen for sustained pain relief. Women also rated naproxen higher for overall symptom relief and were more likely to prefer it over the alternatives.
That said, a separate double-blind crossover study of 57 women found ibuprofen provided greater peak pain relief than naproxen sodium. The practical takeaway: both drugs work well for cramps, but they perform differently at different time points. Ibuprofen may hit harder in the first couple of hours, while naproxen holds its advantage longer because of its extended duration. With a half-life of about 15 hours, naproxen keeps working in your system far longer than ibuprofen’s roughly 4 to 6 hours, meaning fewer doses throughout the day.
Acetaminophen is the weakest option of the three for cramps. It reduces pain signaling but does not block prostaglandin production in the uterus the way naproxen and ibuprofen do, so it doesn’t address the root cause of menstrual pain.
When and How to Take It
Timing matters more than most people realize. The best results come from starting naproxen a day or two before your period begins, or at the very first sign of bleeding or cramping. This preemptive approach blocks prostaglandin buildup before contractions ramp up, rather than trying to suppress them after pain has already started.
The NHS recommends a starting dose of 500 mg, followed by 250 mg every 6 to 8 hours as needed. After the first day, the maximum is 1,250 mg in 24 hours (five 250 mg tablets). Most people only need naproxen for one to three days per cycle. Because it lasts so long, you typically need just two or three doses a day compared to the every-four-hours schedule that ibuprofen often requires.
Take naproxen with food or a glass of milk to reduce the chance of stomach irritation. If you’re buying it over the counter, you’ll often find naproxen sodium (sold as Aleve), where two tablets equal roughly 440 mg of naproxen sodium. Follow the package directions for the OTC version, which uses slightly different dosing than the prescription form.
Side Effects to Watch For
The most common side effects are gastrointestinal: nausea, heartburn, gas, constipation, or diarrhea. These are usually mild and short-lived when you’re only taking naproxen for a few days each month. The more serious risks, like stomach ulcers or intestinal bleeding, are primarily a concern with long-term daily use, higher doses, or in people who smoke, drink heavily, or are over 65.
Stop taking naproxen and get medical attention if you notice stomach pain that doesn’t go away, vomit that looks bloody or like coffee grounds, or black tarry stools. These can signal internal bleeding.
You should avoid naproxen if you’ve recently had a heart attack, have a history of stomach ulcers or intestinal bleeding, have kidney disease, or are pregnant at 20 weeks or beyond. If you’re allergic to aspirin or ibuprofen, naproxen is off the table too, since they belong to the same drug class.
When Cramps Have an Underlying Cause
Standard period cramps (primary dysmenorrhea) respond well to naproxen on their own. But if your cramps are caused by an underlying condition like endometriosis or fibroids, naproxen can still help with pain, though it may not be enough by itself.
For endometriosis-related pain, the same preemptive timing applies: start naproxen several days before your period to block the prostaglandin formation that drives endometriosis pain and inflammation. The recommended approach is to use the highest dose you tolerate comfortably. If one type of anti-inflammatory doesn’t help after four to six weeks, it’s worth trying a different one, since individual responses vary. Many people with endometriosis end up combining naproxen with hormonal treatments for better overall control.
If your cramps are severe enough that over-the-counter naproxen doesn’t make a noticeable dent, that itself is useful information. Cramps that don’t respond to anti-inflammatories can be a sign of secondary dysmenorrhea, where something beyond normal prostaglandin activity is driving the pain.