Period cramps are caused by your uterus contracting to shed its lining, driven by hormone-like chemicals called prostaglandins. The more prostaglandins your body produces, the stronger the contractions and the worse the pain. Anywhere from 16% to 91% of people who menstruate experience cramps, and roughly 7% to 15% deal with pain severe enough to interfere with daily life.
How Prostaglandins Trigger Cramps
Every menstrual cycle follows the same hormonal script. After ovulation, progesterone rises to maintain the uterine lining in case of pregnancy. When pregnancy doesn’t happen, progesterone levels drop sharply. That drop is the trigger for menstruation, and it sets off a cascade of chemical signals in the uterine lining.
As the lining begins to break down, it releases prostaglandins, particularly one called prostaglandin F2α. Unlike other related compounds that cause a contraction followed by relaxation, F2α consistently stimulates the uterine muscle to contract. These aren’t gentle squeezes. The contractions compress the blood vessels that feed the uterine wall, temporarily cutting off oxygen to the tissue. That oxygen deprivation produces waste products that activate pain-sensing nerve fibers (called type C pain neurons), creating the deep, achy cramping you feel in your lower abdomen. It’s the same basic mechanism behind a muscle cramp anywhere in the body: contraction, reduced blood flow, pain.
Prostaglandin levels are highest during the first one to two days of your period, which is why cramps tend to peak early and then ease off. People with more intense cramps generally have measurably higher concentrations of prostaglandins in their menstrual fluid.
Why Some People Get Worse Cramps
Not everyone produces the same amount of prostaglandins, and several factors influence how severe your cramps are. Starting your period at age 11 or younger is linked to more severe and longer-lasting cramps. Having longer menstrual cycles (around 35 days rather than the typical 28 to 29) also increases the likelihood. Higher body weight raises the odds of cramps by about 75%, based on research from the University of Michigan.
Smoking makes a measurable difference too. Current smokers have roughly a 50% increase in their odds of experiencing pain lasting more than two days. Drinking alcohol during an episode of cramping tends to worsen both the severity and duration of the pain. These factors don’t cause cramps on their own, but they amplify the underlying prostaglandin-driven process, likely by affecting blood flow or inflammation levels in the uterus.
Age works in your favor over time. Cramps often become less severe after your mid-20s and may improve significantly after pregnancy, likely because the uterus changes structurally and in how it responds to prostaglandins.
When an Underlying Condition Is the Cause
Most period cramps fall into the “primary” category, meaning they’re a normal (if miserable) part of menstruation with no underlying disease. But cramps that get progressively worse over time, appear for the first time after years of relatively painless periods, or don’t respond to typical pain relief may point to a secondary cause. Common culprits include endometriosis, adenomyosis, and uterine fibroids.
Adenomyosis happens when the tissue that normally lines the inside of the uterus grows into the muscular wall itself. During your period, that embedded tissue also thickens, breaks down, and bleeds, but it has nowhere to go. The result is a swollen, enlarged uterus and sharp, severe cramping. Its growth depends on estrogen, so it tends to affect people in their 30s and 40s and improves after menopause.
Endometriosis involves similar tissue growing outside the uterus entirely, on the ovaries, fallopian tubes, or pelvic lining. It responds to the same hormonal cycle, causing inflammation and pain that often extends beyond the period itself. Fibroids are noncancerous growths in the uterine wall that can distort the muscle and increase cramping, especially during heavy periods.
Signs that your cramps may have a secondary cause include pain that worsens year over year, unusually heavy or irregular bleeding, pain during sex, and vaginal discharge. If standard treatment hasn’t helped after three to six months, further evaluation with a pelvic exam and ultrasound can check for these conditions.
How Pain Relievers Work on Cramps
Over-the-counter anti-inflammatory pain relievers like ibuprofen and naproxen target period cramps at their source. They block an enzyme called cyclooxygenase, which your body needs to produce prostaglandins. Fewer prostaglandins means fewer and weaker uterine contractions, less blood vessel constriction, and less pain signaling. This is why these medications work better for period cramps than acetaminophen (Tylenol), which reduces pain perception but doesn’t affect prostaglandin production.
Timing matters. Taking an anti-inflammatory at the first sign of cramping, or even just before your period starts if you can predict it, prevents the prostaglandin buildup before it reaches full force. Waiting until the pain is already intense means the chemicals are already circulating and harder to counteract.
Hormonal birth control is another common approach, particularly for people whose cramps don’t respond well to pain relievers alone. By suppressing ovulation or thinning the uterine lining, hormonal methods reduce the amount of tissue that breaks down each cycle, which means less prostaglandin release overall. This is also why some people notice lighter cramps on the pill, a hormonal IUD, or other hormonal contraceptives.
What Cramp Pain Actually Feels Like
Period cramps typically produce a dull, throbbing ache in the lower abdomen that can radiate to the lower back and inner thighs. The pain comes in waves, matching the rhythm of uterine contractions. Some people also experience nausea, loose stools, or dizziness during their worst cramps. These symptoms aren’t coincidental: prostaglandins don’t stay neatly confined to the uterus. They circulate and can affect smooth muscle throughout the body, including the digestive tract, which is why your gut often feels off during the first day or two of your period.
For most people, cramps are worst in the first 24 to 48 hours as prostaglandin levels peak, then taper off as the lining finishes shedding. If your pain extends well beyond day two or three, persists between periods, or has been escalating over several cycles, that pattern is worth paying attention to.