Menarche (say "MEN-ar-kee") is a girl's first menstrual cycle. A first period usually happens after several years of pubic hair growth, breast development, and rapid growth known as a "growth spurt." Menarche most commonly happens sometime between ages 11 and 14.⁶ It normally happens as early as age 9 or up to age 15. If you are a teenage girl, see your doctor if you have not started having periods by age 15.

The first menstrual cycles are usually light and unpredictable. During the first 2 years, a typical teenage menstrual cycle can be as short as 21 days or as long as 45 days.² About 2 out of 3 girls have a regular pattern of menstrual periods within 2 years of menarche.⁷

Long, heavy periods are fairly common during the teen years. The hormone (endocrine) system is still maturing, and progesterone levels aren't always high enough during regular cycles to help the uterine lining (endometrium) break down. When the endometrium has built up for too long, heavy menstrual bleeding follows. This type of bleeding usually gets better on its own, without treatment. But see a doctor for menstrual bleeding that lasts longer than 7 days or for cycles that are shorter than 21 days or longer than 45 days. For more information, see the topic Dysfunctional Uterine Bleeding.

For teens

Ask an adult you trust for advice on using feminine products, such as tampons or pads, when you have menstrual bleeding. Always keep a pad or tampon handy in your purse or backpack.

Tampons fit inside your vagina and are good to use when swimming or doing other physical activities. Pads have adhesive strips on them that stick to your underwear. Be sure to change tampons or pads regularly. Having a period won't prevent you from doing any of the activities you normally do, and no one will be able to tell when you're having one.

If you have cramps with your period, you can get some relief with regular exercise, a heating pad, a warm bath, and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or naproxen. An NSAID is likely to make regular cramps go away completely. (If you are younger than 20, do not take aspirin. Aspirin increases the risk of Reye syndrome, a disease that affects the brain and liver.) If these treatments don't help, talk to your doctor about prescription medicines.

For more information, see the topic Menarche.