Periods in the teen years are often irregular, and many girls and their parents aren’t sure what’s normal. Heavy periods are one of the most common reasons teens run low on iron, and low iron can cause tiredness and trouble concentrating that get blamed on something else. This guide covers what’s normal, what isn’t, and what to do about it.

The short version

  • Teen girls need a lot of iron. The NIH recommends 15 mg a day for girls 14 to 18 and 8 mg a day for girls 9 to 13, partly to make up for iron lost in periods.
  • Heavy periods can drain iron. Iron deficiency, with or without anemia, is common in young women with heavy menstrual bleeding.
  • Even without anemia, low iron matters. It can cause tiredness and trouble with learning and memory, according to the American College of Obstetricians and Gynecologists (ACOG).
  • Know the warning signs: bleeding through a pad or tampon in 2 hours or less with most periods, or periods that last 7 days or more.
  • See a doctor if those signs sound familiar. About 1 in 5 teens with heavy periods has an underlying bleeding disorder.
  • Don’t start iron pills on your own. A blood test shows whether you need them.

Why teen girls are at higher risk

Three things add up: a growing body that needs more iron, monthly blood loss, and diets that may be low in iron, especially for girls who eat little meat. The NIH lists teen girls and women with heavy periods among the groups most likely to have trouble getting enough iron. It also says vegetarians who don’t eat meat, poultry, or seafood need almost twice as much iron, because iron from plants is absorbed less well.

What’s a normal period, and what isn’t

ACOG’s guidance, as summarized by the American Academy of Family Physicians, says:

  • Normal for teens: a cycle every 21 to 45 days, with bleeding that lasts 7 days or fewer. Cycles can be irregular in the first couple of years after a girl’s first period.
  • Not “normal for teens”: soaking through a pad or tampon in 2 hours or less with most periods, bleeding through onto clothes or sheets, or periods that last 7 days or more.

ACOG defines heavy menstrual bleeding as bleeding that lasts more than 7 days or involves more than 80 mL of blood in a cycle. Because it’s hard to measure blood loss at home, the pad-and-tampon signs above are the practical way to spot it. If heavy periods run in your family, they can start to feel normal, so it’s worth asking even if no one else has mentioned it.

Signs of low iron

Headaches and tiredness are common when heavy periods lead to iron deficiency anemia, according to the AAFP’s summary of ACOG’s guidance. Even without anemia, depleted iron can cause fatigue and trouble with thinking, especially verbal learning and memory. The NIH says people with iron deficiency anemia are less able to fight off infections, to work and exercise, and to control their body temperature. Because these look like ordinary teenage tiredness, a blood test is the way to know.

Testing

ACOG recommends that teens with heavy periods be checked for anemia from blood loss, including a ferritin test, which shows your iron stores. A normal or high ferritin doesn’t always rule out low iron, because inflammation can raise it, according to the AAFP summary. Ask your doctor what your results mean, and see Iron Levels in Pregnancy for how the tests work.

What helps

  • Treat the cause, not just the iron. Doctors have ways to reduce heavy bleeding. Replacing iron without addressing heavy periods can leave you running low.
  • Look for a bleeding disorder. About 20% of teens with heavy periods have an underlying bleeding disorder, and half of girls with one have heavy periods from their very first. ACOG suggests asking about a family history of bleeding disorders or of treatment for anemia, and about periods that last 7 days or more with flooding.
  • Iron foods with vitamin C. Beans, lentils, lean meat, and fortified cereals help, and so do citrus, strawberries, and peppers eaten at the same meal. See Iron-Rich Foods for Pregnancy and How to Absorb More.
  • Supplements only with your doctor. Iron pills can cause constipation and an upset stomach, the right dose depends on your blood tests, and the upper limit for teens is 45 mg a day from all sources, according to the NIH. Keep iron supplements away from younger siblings, because iron is a leading cause of fatal poisoning in children under 6.
  • If you’re vegetarian or vegan, plan iron on purpose and ask whether to check your ferritin.

Folic acid for teens

The CDC and the NIH recommend that all women and teen girls who could become pregnant get 400 mcg of folic acid a day, from supplements, fortified foods, or both. Nearly 1 in 5 girls ages 14 to 18 don’t get enough folate, even counting supplements, according to the NIH, so a daily multivitamin with folic acid is an easy habit to start. Most people in the U.S. get enough folate from food, according to the NIH, so for younger girls the usual advice is food first. Check with the pediatrician before starting a supplement. See Folic Acid at Every Stage of Life.

When to see a doctor

  • Periods that soak a pad or tampon in 2 hours or less with most periods, or that last 7 days or more.
  • Heavy periods along with constant tiredness, headaches, or trouble concentrating.
  • Bleeding heavy enough that you miss school or activities.
  • A family history of heavy periods, a bleeding disorder, or anemia.
  • Dizziness, fainting, or shortness of breath with a heavy period. Get medical care that day.

What to do now

  • Track your periods for a few months: how many days, and how often you change a pad or tampon.
  • Bring the notes to your doctor and ask about a ferritin test.
  • Add an iron food and a vitamin C food to each meal.
  • Don’t start iron pills without a blood test and a doctor’s advice.

Related reading

Sources

Updated November 2026. This article is for general information and is not a substitute for advice from your health care provider.