Period cramps are pain in your lower abdomen caused by your uterus contracting to shed its lining during menstruation. About 71% of people who menstruate experience them, making cramps one of the most common physical symptoms of having a period. The pain typically starts one to three days before your period begins, peaks about 24 hours after bleeding starts, and fades within two to three days.
Why Your Uterus Cramps
As your uterine lining breaks down each month, the tissue releases chemical messengers called prostaglandins. These prostaglandins do two things: they trigger the muscular wall of the uterus to contract (squeezing the lining out), and they constrict the blood vessels feeding the uterine muscle. That combination of intense squeezing and reduced blood flow starves the tissue of oxygen temporarily, similar to what happens when a muscle cramp hits your calf during exercise. The oxygen-deprived tissue produces waste products that irritate nearby pain fibers, which is what you actually feel as cramping pain.
People with more severe cramps tend to have higher levels of prostaglandins. This is why anti-inflammatory pain relievers work so well for period cramps: they block the production of prostaglandins at the source, reducing both the contractions and the oxygen deprivation that drives the pain.
What Period Cramps Feel Like
Most people describe cramps as a dull, throbbing ache in the lower abdomen, sometimes radiating into the lower back or inner thighs. The pain comes in waves as the uterus contracts and relaxes. Some cycles are worse than others, and cramps tend to be more intense during heavier flow days.
Cramps often come with other symptoms: bloating, nausea, fatigue, loose stools, or headaches. The loose stools happen because the same prostaglandins that contract your uterus can also stimulate your intestines.
Normal Cramps vs. Something More
Normal period cramps are uncomfortable but manageable. They shouldn’t regularly force you to miss work, school, or daily activities. If they do, that’s worth paying attention to, because severe cramps can signal an underlying condition.
The most common culprit is endometriosis, where tissue similar to the uterine lining grows outside the uterus. Endometriosis pain often starts before your period and extends well after it ends. It can also cause pain during sex, pain with bowel movements, fatigue, and fertility problems. Fibroids (noncancerous growths in the uterine wall) are another common cause of cramps that are more intense than typical.
A few patterns suggest your cramps deserve medical evaluation: pain lasting longer than three days, cramps that have gotten significantly worse over time, very heavy bleeding alongside the pain, or pain that occurs outside your period altogether. These don’t necessarily mean something is wrong, but they’re worth investigating.
Pain Relief That Works
Anti-Inflammatory Medications
Over-the-counter anti-inflammatory pain relievers like ibuprofen and naproxen are the most effective option for most people. They work by lowering prostaglandin production, which means they reduce the underlying cause of the pain rather than just masking it. The key is timing: taking them when cramps first start (or even just before your period begins, if your cycle is predictable) works better than waiting until the pain is already intense. Once prostaglandins have already flooded the tissue, it’s harder to get ahead of the pain.
Heat Therapy
A heating pad or adhesive heat patch on your lower abdomen is surprisingly effective. A meta-analysis of clinical trials found that heat patches actually outperformed oral pain medication for reducing menstrual pain severity. Heat relaxes the uterine muscle and increases blood flow to the area, counteracting the oxygen deprivation that drives cramp pain. You can use heat on its own or combine it with pain relievers for stronger relief.
Exercise
Moving your body is probably the last thing you want to do when you’re cramping, but moderate exercise increases blood flow to the pelvis and triggers your body’s natural pain-relieving chemicals. Even a 20-minute walk or some gentle stretching can take the edge off.
Vitamins and Supplements
Several vitamins have shown genuine promise in clinical trials for reducing cramp severity over time, though they’re not quick fixes like pain relievers.
Vitamin B1 (thiamine) performed comparably to ibuprofen in one study of 152 people with moderate to severe cramps. Those taking 100 mg of B1 daily saw similar pain reduction to those taking 400 mg of ibuprofen, with the B1 group showing even greater improvement by the second and third months.
Vitamin D has been studied in people who are deficient, and high-dose supplementation significantly reduced pain over a two-month period compared to placebo. If you suspect you’re low in vitamin D (common in people who get limited sun exposure), correcting the deficiency may help your cramps.
Vitamin E at 200 units daily reduced both pain severity and pain duration in a trial of 278 teenagers compared to placebo, with benefits appearing at two months and holding at four months. Fish oil has also shown modest benefits, and combining it with vitamin B1 may work better than either alone.
Why Some Periods Cramp Worse Than Others
Your prostaglandin levels aren’t identical every cycle, which is why some months feel fine and others knock you flat. Stress, sleep deprivation, and inflammation from diet or illness can all influence prostaglandin production. Cramps also tend to be most severe during adolescence and the early twenties, often improving with age or after childbirth. Hormonal birth control reduces cramps for many people by thinning the uterine lining, which means less tissue to shed and fewer prostaglandins released.
If your cramps have always been manageable but suddenly become severe, or if they start showing up for the first time in your thirties or forties, that shift is more likely to point toward a new structural issue like fibroids or endometriosis rather than normal variation.