When it comes to avoiding pregnancy, there are many birth control options available. Whether you’re curious about the pill or seeking information on alternatives like the implant, IUD, or patch, there is no universal solution for selecting the best birth control method for you.

The birth control pill remains the most commonly prescribed form of contraception in the U.S., according to an analysis by the CDC’s NCHS.

Dr. Lonna Gordon, MD, the head of Adolescent Medicine at Nemours Children’s Hospital in Orlando, Florida, explains that birth control pills are “daily pills taken to prevent pregnancy.”

Curious about what to expect before starting the pill? In a discussion with YSL News, a medical professional answers your key questions.

Using the birth control pill

There are two main categories of birth control pills: combination oral contraceptive pills and progestin-only pills, says Dr. Gordon.

Combination pills are available in various dosing packs, containing “active” pills with hormones and “inactive” (hormone-free) pills that are taken throughout the month, according to the Cleveland Clinic. Typically, these packs come in cycles of 21-day, 24-day, or 28-day. The naming conventions relate to how many days contain active hormones versus placebo pills, Dr. Gordon explains.

In contrast, progestin-only pills usually come in 28-day packs, says Dr. Gordon. For this type of pill, taking it at the exact same time every day is crucial for maintaining its effectiveness, as there is a very narrow window for missed doses.

Adjusting to the pill

Your body naturally produces hormones, so when you start taking the birth control pill, it adjusts the hormone production based on what the pill provides. Dr. Gordon recommends allowing two to three cycles for the body to adapt to the pill.

Once the pill reaches full efficacy, it does more than just prevent pregnancy; it can also improve skin clarity for those dealing with hormonal acne. For individuals with severe menstrual cramps, the pill may lighten periods, thereby reducing menstrual pain, according to Dr. Gordon. Additionally, taking the pill may decrease the risk of uterine and ovarian cancers and can be prescribed to manage endometriosis, as noted by the Cleveland Clinic.

When does the pill start working?

After beginning the pill, you’ll need to wait about a week before it provides protection against pregnancy, says Dr. Gordon.

However, the time required for the pill to become fully effective varies based on whether you take a combination or progestin-only pill, as well as your position in your menstrual cycle.

For combination pills, if you start taking them within five days of the beginning of your period, protection begins immediately. On the other hand, if you start any other time during your cycle, you will not be protected against pregnancy until a week after starting the pill, as outlined by Planned Parenthood.

The progestin-only pill becomes effective after two days of use, according to Mount Sinai.

Effectiveness of the pill

Dr. Gordon emphasizes the importance of distinguishing between perfect use and typical use when discussing effectiveness.

“When taken correctly, both the combination and progestin-only pills offer 99% effectiveness in preventing pregnancy,” according to the Mayo Clinic. However, the typical use failure rate for both types of pills is around 7%, per the CDC.