It’s normal for your period to change slightly from month to month -- your flow might start a little earlier or later or be a little heavier or lighter. But if your menstrual cycle is all over the place every month, a few things could be to blame.
Pregnancy is the most obvious reason for a missed period, but certain medical conditions, changes in your work or exercise habits, or even stress also can mess with menstruation. And in some cases, so can your prescriptions.
Hormonal Birth Control
Birth control pills or hormonal IUDs typically make your periods lighter, shorter, and more regular. They’re sometimes prescribed as a treatment for women who have endometriosis, a condition that can cause heavy menstrual bleeding and very painful cramps.
However, if you take the progestin-only “mini-pill,” your cycle may be less regular at first. Some women have bleeding in between their regular periods for a few months after starting the medication.
And some women notice missed periods in the months after they stop birth control pills, so if you’re trying to get pregnant, talk to your doctor about anything you think might be unusual.
Hormone Therapy
During perimenopause (the years leading up to menopause), your hormone levels change. This can make your periods unpredictable and often heavier than normal. Hormone therapy (estrogen, progesterone, or a combination of both) can help make your cycle more regular, but be sure to talk about the risks and benefits with your doctor.
Warfarin (Coumadin)
This medication helps prevent blood clots. The biggest issue linked to it is bleeding. If you take this and your menstrual flow is extremely heavy or you bleed in between your periods, it’s important to let your doctor know.
Aspirin and NSAIDs
Aspirin also can help prevent blood clots. That’s why doctors sometimes prescribe it after a heart attack or stroke, which can happen if a blood vessel becomes blocked by a clot. But if you take aspirin regularly, you may notice that your periods are heavier or longer than usual. If you have more bleeding than normal, talk to your doctor.
Other painkillers known as nonsteroidal anti-inflammatory drugs (NSAIDs), which include ibuprofen and naproxen, have been shown to have the opposite effect. They can make the flow lighter during your period.
Thyroid Medication
Your thyroid is a gland that makes certain hormones. If it doesn’t make enough -- a condition called hypothyroidism -- your periods can be irregular.
One drug people take to treat hypothyroidism is called levothyroxine (Levoxyl, Synthroid). It replaces the hormones normally made by your thyroid, and it can cause changes in your period. Talk to your doctor if the changes cause problems for you or don’t go away.
Antidepressants
Researchers have found that some women who take antidepressants have menstrual disorders like painful cramps, heavy bleeding, or missed periods as side effects. You’re most likely to notice unusual periods in the first 3 months after you start the medication but talk to your doctor if they don’t get back to normal after that.
If your premenstrual symptoms are so serious that they affect your daily life -- a condition called premenstrual dysphoric disorder (PMDD) -- antidepressants may actually help.
Epilepsy Medication
Studies of women who have epilepsy and take anti-epilepsy drugs have shown that many have missed or irregular periods or changes in the length of their cycles. Tell your doctor if you have those kinds of side effects; they may want to make sure you don’t have a condition such as polycystic ovary syndrome, especially if you want to get pregnant.
Chemotherapy
This cancer treatment can throw your cycle out of whack and make your periods irregular or your flow heavier. Sometimes your periods may stop altogether. But your periods may come back within a year or more, especially in younger women.
