The first oral contraceptive approved for over-the-counter use in the United States will become available in stores and online this month. The medication, known as Opill, has a manufacturer’s suggested retail price of $19.99 for a one-month supply and $49.99 for a three-month supply.

Many people may want to know how Opill is different from other birth control methods that are available only with a doctor’s prescription. How effective is this medication, and what are the side effects? Who can take it, and who should not? And why is it still important to visit your gynecologist or primary care provider if you use this medication?

To guide us through these questions, I spoke with CNN wellness expert Dr. Leana Wen. Wen is an emergency physician and adjunct associate professor at George Washington University. She previously served as the health commissioner of Baltimore, where she oversaw the city-run reproductive health clinics.

CNN: What is Opill, and how does it differ from other oral birth control methods?

Dr. Leana Wen: There are two main forms of oral contraception. One is the combination birth control pill, which contains both estrogen and progestin. The second is a pill that contains only progestin.

Opill is the second type of pill and contains only progestin. In July, the US Food and Drug Administration approved Opill for over-the-counter use, meaning that people who want to use this form of oral contraception no longer have to get a prescription; they can go directly to the pharmacy or to an online pharmacy retailer to buy this medication.

Although this pill was recently approved for over-the-counter use, it is not a new medication. The FDA approved Opill under a different name in 1973. We have experience with this medication.

CNN: How effective is Opill at preventing pregnancy?

Wen: When people use Opill as the manufacturers intend, meaning taking one pill at the same time every day, Opill is 98% effective at preventing pregnancy.

This is what’s referred to as “perfect use.” “Typical use” is more indicative of how most people use the pills in real life, and it considers that some people may forget a dose or sometimes take it at a different time than they should. With typical use, Opill is about 91% effective.

CNN: What should people do if they miss a dose or are late taking it?

Wen: People who miss a dose should take the missed pill as soon as they remember. If it’s more than three hours late, they should use an additional method of birth control — for example, a barrier method like condoms — for at least the next 48 hours.

Individuals who want additional protection against pregnancy should consider using both the pill and barrier methods. And, of course, barrier methods offer protection against sexually transmitted infections, which birth control pills alone do not.

CNN: Who should consider taking Opill, and who should not?

Wen: Opill should be considered by individuals who desire birth control but are unable to see a primary care physician, gynecologist or other provider who can prescribe birth control pills. The medication should not be used by people who have ever had or currently have breast cancer.

There are some drug interactions such that people on certain medications should not take Opill. These medications include certain seizure medications like carbamazepine and phenytoin, barbiturates such as phenobarbital, HIV medications like efavirenz and fosamprenavir, and herbal preparations that contain St. John’s wort.

While Opill can be combined with barrier contraceptive methods like condoms, it should not be used by people who are already on other hormonal birth control products such as another contraceptive pill, implant, injection or patch. The medication should not be taken by people who have had missed periods and could be pregnant. Opill is not an emergency contraceptive and does not prevent pregnancy after unprotected sex.

CNN: A lot of people think they shouldn’t take oral contraceptives because of the risk of blood clots. Is this true?

Wen: Birth control pills containing both estrogen and progestin are associated with a small risk of blood clots. But progestin-only pills like Opill are not associated with a higher risk of blood clots. That means people who are at higher risk of blood clots, who are often not able to take combination pills, could be eligible for progestin-only pills.

CNN: Is there an age limit to who can take Opill?

Wen: Opill is available over-the-counter without an age restriction. That means people who have started menstruating and individuals going through perimenopause can purchase it.

CNN: What are the side effects?

Wen: The most commonly reported side effects of Opill include irregular vaginal bleeding or unexpected spotting, cramps, bloating, headache and nausea. Some people experience acne, increased appetite and weight gain.

Individuals who experience these side effects should consider consulting a medical provider. They may need to switch to another form of oral contraceptive or another birth control method.

CNN: There are some critics who argue that people should be required to visit their doctor before getting birth control pills. Are they right?

Wen: According to the American College of Obstetricians and Gynecologists, “pelvic and breast examinations, cervical cancer screening, and sexually transmitted infection screening are not required before initiating hormonal contraception and should not be used as reasons to deny access to hormonal contraception.” ACOG has issued a statement specifically in support of Opill and included additional clinical guidance for patients and providers.

Other major medical associations that support making oral contraception available without a doctor’s prescription include the American Medical Association and American Academy of Family Physicians.

In an ideal world, of course, people should go to their provider. The problem is that, in the United States, more than 19 million reproductive-age women live in contraceptive deserts. Nearly 8 million women of reproductive age are uninsured. In the US, nearly half of all pregnancies are unintended. Those who are in favor of improved access to contraceptives would argue that greater availability could reduce the rate of unintended pregnancies.

CNN: Why is it still important for people using Opill to visit the gynecologist or primary care provider?

Wen: This is a crucial point. Everyone should have a primary care provider, including women of reproductive age. Ideally, everyone should seek to visit their primary care provider every year. Reasons for doing this include preventive care such as cancer screening, testing for sexually transmitted diseases and blood pressure checkups. People with chronic illnesses such as asthma and diabetes also need ongoing care.

Opill being sold without a prescription should not discourage people who otherwise would have gone to their primary care provider from doing so. Rather, the over-the-counter contraceptive offers an additional avenue for pregnancy prevention for individuals who have difficulty accessing medical care.