When you’re on your period, your body is shedding the uterine lining it spent the previous weeks building up. Estrogen and progesterone, the two hormones that thickened that lining in preparation for a possible pregnancy, have dropped sharply. That hormonal crash is what triggers bleeding, but it also sets off a chain of effects throughout your body, from cramps and digestive changes to mood shifts and fatigue. Here’s what’s actually going on and how to deal with it.
Why Your Uterus Hurts
Cramps are the most common complaint during a period, and they have a straightforward cause. As progesterone levels fall, your body releases fatty acids called prostaglandins. These chemicals tell the smooth muscle of your uterus to contract, squeezing out the lining. That alone would be uncomfortable, but prostaglandins also narrow the blood vessels feeding the uterus, temporarily cutting off oxygen to the tissue. The combination of strong contractions and reduced blood flow is what creates that deep, aching pain in your lower abdomen.
Prostaglandins don’t stay neatly contained in your uterus. They circulate and can trigger headaches, nausea, and even vomiting. The intensity varies from person to person and cycle to cycle, largely depending on how much prostaglandin your body produces. People with more severe cramps tend to have measurably higher prostaglandin levels in their menstrual fluid.
What’s Normal for Bleeding
A typical period lasts between three and seven days. Total blood loss for a normal period is under 60 milliliters for the entire cycle, which is roughly four tablespoons. Moderately heavy periods fall between 60 and 100 milliliters, and anything over 100 milliliters is considered excessive. Clinically, the threshold for heavy menstrual bleeding is 80 milliliters per cycle, but interestingly, only about 40 to 50 percent of people who feel their periods are heavy actually exceed that number. Perception of heaviness doesn’t always match measurable volume.
Flow isn’t constant. Most people experience heavier bleeding in the first two or three days, then a tapering off. Clots are normal as long as they’re smaller than a quarter. If you’re soaking through a pad or tampon every hour for several consecutive hours, or passing large clots regularly, that’s worth bringing up with a healthcare provider.
Why Your Digestion Changes
If you notice looser stools or more frequent bathroom trips during your period, prostaglandins are the culprit again. The same chemicals that contract your uterine muscles can act on the smooth muscle of your intestines, speeding up movement through the bowel. The result: softer stools, more urgency, and sometimes outright diarrhea in the first day or two of your period.
The timing lines up with what’s been happening hormonally in the days before. Progesterone, which peaks after ovulation, tends to slow down your gut. That’s why some people feel bloated or constipated in the days leading up to their period. Once progesterone drops and prostaglandins rise, the pendulum swings the other way. This shift from constipation to loose stools is a predictable pattern for many people, not a sign that something is wrong.
Mood, Energy, and Sleep
The drop in estrogen at the start of your period can pull serotonin levels down with it. Serotonin is one of the brain’s primary mood regulators, so lower levels can leave you feeling irritable, flat, or more emotional than usual. For most people, this is mild and resolves within a few days as hormone levels start climbing again in the follicular phase.
Fatigue during your period is also common and comes from multiple directions. Blood loss itself can be mildly draining, especially on heavier days. Pain disrupts sleep. And the low-hormone state of menstruation means you’re at the bottom of your cycle’s energy curve. This isn’t the time to push yourself to peak performance. Lighter days and more rest aren’t laziness; they’re a reasonable response to what your body is doing.
Managing Cramps Effectively
Over-the-counter anti-inflammatory pain relievers work well for period cramps because they directly block prostaglandin production. The key is timing: taking them at the first sign of cramping, or even just before your period starts if you can predict it, is far more effective than waiting until pain is already intense. Once prostaglandins have been released and the pain cycle is in full swing, it’s harder for medication to catch up.
Heat is another reliable option. A heating pad or hot water bottle on your lower abdomen relaxes the uterine muscle and increases blood flow to the area, counteracting the vasoconstriction that prostaglandins cause. Many people find that combining heat with a pain reliever works better than either alone.
Exercise helps too, even though it’s often the last thing you feel like doing. Regular aerobic exercise, around 30 minutes three times a week, has been shown in clinical trials to reduce both the severity and duration of menstrual pain over time. You don’t need to run a 5K on day one of your period. A brisk walk, gentle cycling, or yoga with movement can be enough to boost circulation and trigger your body’s own pain-relieving endorphins.
Choosing Period Products
The right product depends on your flow, comfort level, and how often you want to deal with changes throughout the day.
- Tampons absorb 15 to 20 milliliters depending on size and need to be changed every four to eight hours. Current guidelines recommend not leaving a tampon in for more than eight hours, and avoiding wearing them overnight. Using the lowest absorbency that handles your flow reduces the already-small risk of toxic shock syndrome.
- Pads are external, come in a wide range of absorbencies, and carry no TSS risk. They’re the simplest option for overnight use and lighter-flow days.
- Menstrual cups are reusable silicone cups that sit inside the vaginal canal and collect rather than absorb fluid. They hold about 30 milliliters on average, with high-capacity versions holding up to 50 milliliters. That’s roughly double what a super tampon absorbs, meaning longer wear time between empties.
- Menstrual discs sit higher, tucked behind the pubic bone, and can hold 30 to 70 milliliters depending on anatomy and positioning. Some discs can partially self-empty when you use the bathroom, extending their wear time further.
- Period underwear has built-in absorbent layers and works well as backup protection or as a standalone option on lighter days.
What Makes Some Periods Worse
Not every cycle feels the same, and several factors can make a particular period more painful or heavier than usual. Stress raises cortisol, which can disrupt the balance of reproductive hormones and lead to more irregular or intense periods. Poor sleep in the luteal phase (the two weeks before your period) can amplify pain sensitivity. Dehydration makes cramps feel worse because it reduces blood volume, intensifying the ischemia that prostaglandins are already causing.
If your periods have gotten progressively heavier or more painful over time, or if they’re severe enough to regularly keep you home from work or school, that pattern can point to conditions like endometriosis, fibroids, or adenomyosis. These are treatable, and a persistent change in your baseline is a meaningful signal worth investigating.