One drug can have many contradictory uses.

When it comes to taking care of your health, asking questions never hurts. But is it always worth a visit to your doctor? We’re asking experts to weigh in on your burning questions—from feminine to general health and everything in between—so you can get advice from a pro before you go. The doctor will see you now.

The first time my friend heard about progesterone, her gynecologist had casually mentioned that, by the looks of her cervix, she might need to take it before and during pregnancy—if and when the time came. She didn’t think much of it until years later when she miscarried and was diagnosed with polycystic ovarian syndrome (PCOS). Her OB-GYN prescribed progesterone and, a year later, she was able to conceive and carry her baby near full term. It sounds like a newfangled miracle drug for women with feminine health issues, but progesterone supplements have been used to treat feminine health issues since the late 1920s.

If you are curious about progesterone and want to know if it might help you, here’s what you need to know.

Progesterone Is Key to a Healthy Menstrual Cycle

Progesterone, a hormone produced during a woman’s monthly cycle, plays a significant role in preparing her body for pregnancy. After ovulation, a rise in progesterone thickens the uterine lining, so that if she conceives, the fertilized egg will have a healthy place to implant and thrive.

A drop in progesterone triggers the uterus to shed its lining and start a period. When that drop comes too soon, cycles are irregular and other symptoms (headaches, mood changes, low libido, weight gain, and so on) may be present too. Women with low levels of progesterone can have difficulty maintaining a pregnancy through the first trimester. Low progesterone can also cause irregular bleeding. The good news is, a doctor can prescribe progesterone for these cases.

How Progesterone Supplements Are Produced Changes the Way It Affects the Body

Because of its central role in the health of a woman’s reproductive system, progesterone is commonly prescribed for a number of reasons, including irregular periodspolycystic ovary syndromedifficulty maintaining a pregnancy, and post-menopausal hormone therapy, as well as birth control. How can one substance effectively address such different feminine health issues?

Verily’s resident expert, Dr. A. Nicky Hjort, M.D., OB-GYN, explains, “We use different forms of different progesterones in many different ways to achieve many different goals.” It can be confusing, she says, since it appears to be prescribed to achieve opposing goals—on the one hand, as a form of contraception, and on the other, for the ability to maintain a pregnancy. The major difference is that how the hormone is produced changes how it affects the body when it’s applied.

Micronized Progesterone Is Naturally Derived and Not Used for Contraception

Some women who have experienced miscarriage may have a defect in which the body doesn’t produce enough progesterone to maintain a healthy uterine lining and support an embryo. A dramatic drop in progesterone can also be detected amongst women who suffer from severe PMS symptoms. One course of treatment is a dose of progesterone, usually as a vaginal suppository, beginning soon after ovulation until a day or two before her expected period.

Dr. Hjort notes that this type of micronized progesterone is very different from the kind of progesterone given as contraception. For one, it is derived from plants (specifically yams and soy beans) and more closely matches human progesterone than do the synthetic varieties used in birth control.

Synthetic Progestin Is Used to Prevent Pregnancy and Has Many Names

Synthetic progesterone, called progestins, don’t help maintain a pregnancy. They are used for a wide range of applications including birth control, regulating abnormal bleeding, and for hormone therapy after menopause. Below, Dr. Hjort cites the most commonly prescribed formulations of progestin, though more than forty other types than listed below exist.

  • Norethidrone, commonly referred to as the “mini pill,” is a low-dose, single-hormone contraceptive. The pill is taken daily to suppress ovulation. It also thickens cervical mucus to make it more difficult for sperm to fertilize an egg, lowers the levels of other reproductive hormones, slows the passage of the egg through the Fallopian tubes, and stops the uterine lining from growing.
  • Levonorgestrel is another progestin prescribed as birth control, also known as Plan B when taken orally. It is used to prevent ovulation, prevent fertilization, or prevent a fertilized egg from implanting in the uterus. Mirena administers levonorgestrel over the course of three to five years via an intrauterine device (IUD) inserted by a gynecologist.
  • Etonogestrel is a progestin that comes in two different forms. Nexplanon and Implanon administer etonogestrel over a three-year period via a rod inserted into the upper arm. Etonogestrel acts on the the reproductive system in ways similar to levonorgestrel.
  • Medroxyprogesterone, sold under the name Provera, is used to regulate abnormal bleeding in women of reproductive age and in combination hormone therapy for post-menopausal women. Medroxyprogesterone also acts on the reproductive system in ways similar to levonorgestrel.

Get All the Facts About the Kind of Progesterone You Are Being Prescribed and Why

If your doctor recommends progesterone, you should feel comfortable asking her whether the type she is prescribing is synthetic or natural, as the former tend to elicit more unpleasant side effects (blood clots, changes in cycle flow, depression, among them). Possible less serious side effects of any progesterone supplement include, but aren’t limited to: mild nausea, diarrhea, bloating, stomach cramps; dizziness; mild headache; joint pain; breast pain or tenderness; cough; acne or increased hair growth; changes in weight; or vaginal itching, dryness, or discharge. You’ll need to see your doctor regularly while you take progesterone, so don’t miss any appointments.

Make sure you aren’t being prescribed progesterone to cover up symptoms of a bigger feminine health issue, like endometriosis. If you have abnormal periods, including heavy or painful bleeding, it could be that you have a medical condition, and an IUD or progestin pill won’t heal that underlying condition. They only mask or treat the symptoms. Dr. Hjort tells Verily that taking progestin doesn’t always treat the real underlying problem and, on top of that, can even create a problem you previously didn’t have.

The best way to help you and your doctor find out whether you might need progesterone is to regularly chart your cycle. For a woman with PCOS, for instance, charting should reveal a pattern of long cycles, irregular bleeding, or prolonged cervical mucous production.

Ask your doctor how the specific drug is intended to work in your body and what that might mean for your short- and long-term health. There are options available to help you and your doctor identify the root of the issue you’re looking to treat. It never hurts to ask!