Monophasic birth control is a type of birth control pill that delivers the same level of hormones for 21 or 28 days. For the remaining days of the month, you can either take placebo pills or nothing at all. These are the most widely prescribed type of birth control pills.

Monophasic birth control is a type of oral contraceptive. Each pill is designed to deliver the same level of hormone throughout the entire pill pack. That’s why it’s called “monophasic,” or single phase.

Most birth control pill brands offer 21- or 28-day formulations. The single-phase pill maintains even amounts of hormones through the 21-day cycle. For the final seven days of your cycle, you may take no pill at all, or you may take a placebo.

Monophasic birth control is the most commonly prescribed type of birth control. It also has the widest selection of brands. When doctors or researchers refer to “the pill,” they’re most likely speaking of the monophasic pill.

Some women prefer single-phase birth control because a steady supply of hormones may cause fewer side effects over time. People who use multiphase birth control may experience more side effects from the fluctuating levels of hormones. These side effects are akin to typical hormonal changes experienced during the menstrual cycle, such as mood changes.

Monophasic birth control has been studied the most, so it has the most evidence of safety and efficacy. However, no research suggests one type of birth control is more effective or safer than another.

Side effects for single-phase birth control are the same for other types of hormonal contraceptive.

These side effects include:

  • headache
  • nausea
  • breast tenderness
  • irregular bleeding or spotting
  • mood changes

Other, less common side effects include:

  • blood clots
  • heart attack
  • stroke
  • increased blood pressure

Single-phase birth control pills are safe, reliable, and highly effective if you use them accurately. Accurate use relies on your understanding how and when to take the pill.

Keep these tips in mind for using birth control pills correctly:

Pick a convenient time: You need to take your pill every day at the same time, so pick a time when you’ll be able to stop and take your medicine. It may help to set a reminder on your phone or calendar.

Take with food: When you first start taking the pill, you may want to take it with food to reduce nausea. This nausea will fade over time, so this won’t be necessary for more than a week or two.

Stick to the order: Your pills are designed to work in the order they’re packaged. The first 21 pills in a single-phase package are all the same, but the final seven often have no active ingredient. Mixing these up could leave you at risk for pregnancy and cause side effects like breakthrough bleeding.

Don’t forget the placebo pills: In the final seven days of your pill pack, you’ll either take placebo pills or you won’t take pills. It isn’t necessary for you to take the placebo pills, but some brands add ingredients to those final pills to help ease symptoms of your period. Be sure to start your next pack after the seven-day window has ended.

Know what to do if you miss a dose: Missing a dose happens. If you accidentally skipped a dose, take the pill as soon as you realize it. It’s okay to take two pills at once. If you skip two days, take two pills one day and the final two pills the next. Then return to your regular order. If you forget multiple pills, call your doctor or pharmacist. They can guide you on what to do next.

Check out: Choosing the right birth control pill »

Monophasic birth control pills come in two package types: 21-day and 28-day.

Monophasic birth control pills are also available in three doses: low-dose (10 to 20 micrograms), regular-dose (30 to 35 micrograms), and high-dose (50 micrograms).

This isn’t a complete list of single-strength birth control pills, but it encompasses many of the most commonly prescribed brands:

Ethinyl estradiol and desogestrel:

  • Apri
  • Cyclessa
  • Emoquette
  • Kariva
  • Mircette
  • Reclipsen
  • Solia

Ethinyl estradiol and drospirenone:

  • Loryna
  • Ocella
  • Vestura
  • Yasmin
  • Yaz

Ethinyl estradiol and levonorgestrel:

  • Aviane
  • Enpresse
  • Levora
  • Orsythia
  • Trivora-28

Ethinyl estradiol and norethindrone:

  • Aranelle
  • Brevicon
  • Estrostep Fe
  • Femcon FE
  • Generess Fe
  • Junel 1.5/30
  • Lo Loestrin Fe
  • Loestrin 1.5/30
  • Minastrin 24 Fe
  • Ovcon 35
  • Tilia Fe
  • Tri-Norinyl
  • Wera
  • Zenchent Fe

Ethinyl estradiol and norgestrel:

  • Cryselle 28
  • Low-Ogestrel
  • Ogestrel-28

Learn more: Are low-dose birth control pills right for you? »

Birth control pills can either be monophasic or multiphasic. The primary difference is in the amount of hormones you get throughout the month. Multiphasic pills alter the ratio of progestin to estrogen and the doses during the 21-day cycle.

Monophasic: These pills deliver the same amount of estrogen and progestin each day for 21 days. In the final week, you either take no pills or placebo pills.

Biphasic: These pills deliver one strength for 7-10 days and a second strength for 11-14 days. In the final seven days, you take placebos with inactive ingredients or no pills at all. Most companies color the doses differently so that you know when the pill types change.

Triphasic: As with biphasic, each dose of three-phase birth control is marked by a different color. The first phase lasts 5-7 days. The second phase lasts 5-9 days, and the third phase lasts 5-10 days. Your brand’s formulation determines how long you are on each of these phases. The final seven days are placebo pills with inactive ingredients or no pills at all.

If you’re just starting birth control, a single-phase pill may be your doctor’s first choice. If you try one type of monophasic pill and experience side effects, you may still be able to use a single-phase pill. You’ll just need to try a different formulation until you find one that helps you and is best for your body.

As you are considering your options, keep these things in mind:

Cost: Some birth control pills are currently available for little-to-no cost with prescription insurance; others can be quite expensive. You’ll need this medication monthly, so keep price in mind when weighing your options.

Ease of use: To be most effective, birth control pills should be taken at the same time every day. If you’re worried sticking with a daily schedule will be too difficult, talk about other contraceptive choices.

Efficacy: If taken correctly, birth control pills are highly effective at preventing pregnancy. However, the pill doesn’t prevent pregnancy 100 percent of the time. If you need something more permanent, talk with your doctor about your options.

Side effects: When you first begin the pill or switch to a different option, you may have additional side effects for a cycle or two while your body adjusts. If those side effects don’t subside after the second full pill pack, talk with your doctor. You may need a higher-dose medicine or a different formulation.

Keep reading: Which birth control is right for you? »