When it comes to taking a birth control pill, changes in a person’s menstrual cycle are a common side effect. 

The most common types of birth control prescriptions are combination pills, where estrogen and progesterone are both active ingredients. However, there is a pill option where only one of the two hormones is present. This form of birth control is called progestin-only pills. Unlike combination medications, these “mini pills” only contain progestin, which is a human-made version of the progesterone hormone.

While progestin-only pills are not new pregnancy prevention alternatives, they have recently become more accessible. Opill, a progestin-only pill, made history as the first birth control in the United States approved for purchase in stores without a prescription required from a physician. It’s available at Walgreens, CVS and other retailers nationwide, with prices starting at $19.99 for a one-month supply. 

Although both forms of birth control safely help prevent pregnancy, changes to a person’s menstrual cycle look different for each. Before deciding which pill option to take, it is important to be mindful of the side effects it can have on a person’s body and period.

How Do Progestin-Only Pills Work?

Progestin-only pills work differently than combination pills. Progestin-only medications help to regulate the release of cervical mucus during sex. These pills help prevent pregnancy by thickening the mucus in the cervix. The mucus thickness blocks sperm from entering the uterus, making it more difficult to fertilize the egg. Unlike combination birth control, it is possible to still ovulate while taking progestin-only pills.

Another important point is that progestin-only pills are only highly effective when taken properly. Opill, for example, is 98 percent effective when taken every day at the same time. If taken inconsistently, progestin-only pills lose their effectiveness in preventing pregnancy.

If trying to keep up with taking a daily pill is challenging, there are other progestin-only birth control methods available. A person can receive an injection called Depo-Provera or an implant known as Nexplanon instead.

How Do Combination Pills Work?

Combination birth control pills consist of taking estrogen and progesterone consecutively for three weeks. They also thicken mucus in the cervix and change the uterine lining to prevent pregnancy. These hormones safely stop ovulation. Without ovulation, there is no egg to be fertilized. During that last week, a 21-day birth control pack will contain a row of non-hormonal pills that work as a placebo. That placebo week is when menstrual cycles start, but there are alternative ways that stop periods completely.

The birth control patch and vaginal ring are other combination options to explore if searching for different choices to consider that don’t involve taking the pill.

How Do Both Birth Control Pills Impact Periods?

Physician and The Black OBGYN Project co-founder Rachel Bervell said that the main difference between both birth control options is that progestin-only pills typically cause lighter bleeding and less painful cramps. These pills can also cause irregular bleeding and spotting. When taking Opill, the packaging warns that periods “may be less or more frequent, shorter or longer, lighter or heavier” than before starting it. It was also found that periods stopped for some women taking Opill.

Bervell said that periods tend to be more regular while on combination pills. “People may take the estrogen-progestin combination because of acne, PMS symptoms and irregular periods,” she told 21Ninety. “There are slight nuances as to why a person may want to take a combination birth control pill instead.”  

Additionally, combination pills can help alleviate mood swings and stabilize other emotional symptoms linked with PMS.